Actually, inflation was only part of Spain's problem. When the whole of the Hapsburg money making machine is looked at, Spain was one of the most profitable parts of it. The problem for Spain was that its tax money, rather then being spent on its own improvement, went on fighting expensive and largely futile wars elsewhere in Europe, like the Netherlands. Perhaps if that money had been spent differently, Spain could have gotten much more reward for it.
Nevertheless, to get it as a superpower, its going to need to bind those American colonies much more closely too it. Maybe some more expansion in Asia would be a good idea, which could be facilitated by a more successful Spanish-Portuguese union, but I don't know what the chances for that is.
Actually, successful suppression of Elizabethean England would probably have gone hand in hand with contemporary victory in reconquering the whole of the Netherlands. The most plausible scenario I've seen for Spanish victory in England was put forth by Garret Mattingly in his book
The Armada, from the letters of Duke Parma, who was running the war in the Netherlands. He wanted King Philip to give him the funds he was about to "invest" in the Armada; Parma argued that with that additional level of support, he could make short work of the rest of the Netherlands, then from there move across the Channel to Britain. We can never know if he was right but he was canny and with the resources he had, quite successful. Certainly the Dutch were England's allies, and their seapower along with England's was a huge factor in Spain's defeat. (It wasn't that the Dutch actually engaged the Armada, but everyone on both sides knew they were there, very strong and competent in the Channel waters; had that not been the case because their ports were under Hapsburg control, and still more if a certain amount of Dutch seapower were serving the new restored regime on the other side from OTL, things would clearly have been quite different and much grimmer for Elizabeth).
OTL one reason Philip wanted to attack England in the first place was that the English were aiding the Dutch rebellion and conventional wisdom was that no amount of Hapsburg power on land could quash it without eliminating English help; Parma begged to differ but was overruled.
The Armada was a problematic enterprise in many ways; the sheer distance and hence long time cycles of mustering the fleet and sending it out worked against them because the crews, supplies, and ships were all somewhat deteriorated. (An earlier raid by Drake on Spanish ports contributed to their problems, by depriving the fleet of good wood for making water casks with). Had it been launched from much closer ports, with the Dutch allied navy eliminated as a factor (and most likely, drawn in on the Spanish side to some extent) its chances would be better. OTL the purpose of the Armada was in fact to shield and open a path for an amphibious invasion by Parma from the Lowlands; in the event, Parma had neither suitable ships nor a decent port to embark from, even if he could have afforded to turn his back on the unsettled situation on the Continent. So even had it prevailed at sea, the result would have been abortive--English power would be cracked, its pride badly bruised, but the island would not have fallen, unless a popular pro-Catholic rebellion were thus triggered and successful. With a strong force under the command of someone like Parma landed safely on English shores, the latter might have been plausible enough; without it, or with that force much weaker than Parma would have liked, it's much more dubious though evidently Philip and his supporters hoped for it anyway.
A weak part of Parma's version of the plan was that even with a relatively short passage and at the very least, the elimination of the Dutch as enemies at sea, even a pretty big invasion fleet would have, as eventual OTL events proved, suffered from the technical superiority of English cannon, which had longer range. This was no accident, it was a considered policy of Elizabeth's naval men to develop it. As a policy, word of it surely leaked to Spanish espionage and they knew it was a problem they were going to face. I'm not at home right now and I can't repeat a fine passage Mattingly quoted, of a Spanish naval officer explaining to a papal nuncio that they sailed in "devout hope of a miracle." Because he understood in advance the advantages English firepower would bring them, you see.
Well then, it is possible that with the Dutch subdued and some of them coming over to the Hapsburg service, they too could have mastered longer-range guns, or that Parma would see to it that someone on his side developed the things and supplied them. Or that, accepting they could not match the English in this respect, they devised tactics, possibly very costly ones, to bull through and land the troops anyway. If Parma could get a strong force on English soil without being distracted by unsettled accounts in the Netherlands, it is quite plausible he could indeed raise the anti-Elizabethian rebellion he and various exiled English allies of Philip hoped for, and drive the "English Jezebel" out of London and possibly catch and kill her.
Such a Hapsburg victory, if its long-range results were at very least the neutralization of England as a rival (even if England later slipped out of the dynasty's grasp) and the retention of the whole Netherlands as integral Hapsburg territory, might well lay the groundwork for a Spain that simply remains on top.
I am dubious, thinking that if history teaches us anything, it is that "the times, they are a-changing" and "the slow one now will later be fast;" that victory tends to lead to complacency, that the opportunism of the up-and-coming second or third rate powers of one generation leads to them being the triumphal leaders two or three down the line while the old powers inevitably decline. This could be seen in moralistic terms as suggested above, or simply in terms of blind Darwinian opportunity--strategies that work in some circumstances might not be optimal in others and there is a certain amount of blind luck involved.
Certainly being currently on top gives certain inherent advantages; of inertia at the very least, and a sheer mass of resources, including established connections. It would seem, from the revolving door of Great Powers we observe, that these advantages are never sufficient and the rising new powers eat the lunch of the old order consistently.
So any sort of Spain as first-rate power in 1900 scenario means either bucking this trend with the Hapsburgs or some orderly successor dynasty/regime improbably having some combination of better wisdom or better luck than is the usual lot of an established power, or a new Spain rising like a phoenix from the ashes of old Spain. The latter I think is very improbable, as Spain shorn of its vast colonial empire and connections to the larger Hapsburg continental one doesn't have a lot of inherent advantages to let it pull ahead from a low place past likely successors to its first empire.
So unlikely as I judge it, a Hapsburg-wank, one where the sprawling dynastic realm sees itself as still centered on Spain and not some other department such as Austria or a Hapsburgized Lowlands, seems less of a long shot than a New Spain.
So now, if we take the "Parma gets his way and wins" scenario as the POD, there are still many dangerous waters ahead. Spain might wind up circa 1900 being the prevailing power in a Europe culturally and socially and technologically stunted compared to OTL, an arch-reactionary scenario. Frankly I doubt that; it seems that if the Hapsburgs based in Madrid cannot learn to tame and master the horse of rising European capitalism, it will throw them, as OTL. Therefore we have to figure that somehow, the regime is enlightened enough to foster and guide capitalist development rather than suppress or passively frustrate it. If they are wise enough to let this kind of thing happen in the Netherlands and what parts of Germany and Italy they hold sway over, they probably will see the wisdom of furthering it in Spain itself as well, and in their colonial empire overseas.
If they can do that, I don't see what stops them from eventually gaining full hegemony over all of Europe and all its colonies, and from that basis, by 1900, the world, as a universal Catholic Empire.
One which might well, to be sure, tolerate a certain amount of religious diversity. For Parma to succeed in holding down the Netherlands, he'd have to come to some understanding with the Protestant establishment there. Building on that experience, some sort of accommodation of dissent in Britain might also persist and become traditional; from there, a policy of working with non-Christian establishments in American "pagan" territory and facing Muslim, Hindu, Chinese, and other Asian holdings would serve them well.
But I'd expect that it would be in name and principle at least as Roman Catholic as the British Empire was Anglican; eventually people of very different belief, even atheists, could find an honored and safe prestigious place, but the key to complete success would be to pay at least lip service to the Papacy. Which the regime would have a lot of control over to be sure!