What is your obsession with Vichy France? Why is Germany going to be more reluctant to move through Vichy France than invade Italy? There's no problem here, just a minor inconvenience.
Yes, just a minor inconvenience. One that ties down more troops than in OTL, with a more active resistance, augmented by allied agents and arms. You seem obsessed with the idea that 'only a ground offensive' matters, but an allied Spain means more manpower, more bomber bases, within easy striking distance of northern Italy. You might be able to reach northern Italy from english bases, and bomb her ndustrial heartland, but your going to have to fight your way through masses of defending fighters to and from the targets, without fighter escorts. Now base airforces in Spain, and your ready to hit Corsica. Take Corsica, instead of Sicily, and now you have forward fighter bases, so all your Italian bomber raids can be escorted, and Italy looses her industrial base and transportation network.
Basically, the moment Germany invades Vichy, the plug is out, and the allies can now go into africa as allies, and all the french forces in the west can be brought up to the front line, and the naval units historically destroyed, are instead availible to support the allied med offensive. So yea, just a minor inconvenience, where the allies were historically slow to reach and meet the axis armies in africa, now they meerly have to land reinforcments to help out the french, and with the add bonus of supply ports and airbases within Spanish territory. Hitler buys himself two new fronts instead of none, by violating Vichy neutrality, and the air front in France is going to eat up lots of extra forces that historically never had to be sent there, to say nothing of the losses, and the replacements that will need to be sent, for the rest of the war.
The Pyrenees, outside of the Alps, is probably one of the most defensible lines in Europe. The allies would have no advantage of moment and even the roads leading up to the range are so few that it would provide the defender maximum opportunity to position its defenses.
And these defenses, suck up troops that OTL never had to be there. These defenders are going to need supplies, which are vulernable to air and partisan attacks. The Germans can "Try" to commit small forces to the defense, and hope that the allies cannot plaster the defenders with bombers and fighter sweeps prepratory to attacking, but as you yourself pointed out, the allies can always move troops to France by sea. Both in the med or atlantic, in addition to the historical northern choices. If the allies do decide to launch one or more seaborn incursions, will your blocking forces be able to hold out if attacked from behind and totally cut off from supplies? I have to put this here, to interject a bit of humor.
THIS!
By landing in Spain rather than North Africa you just gave the Germans an opportunity to salvage its forces in North Africa.
Really? Tell me how and, more importantly, why, would the Germans just abandon africa the moment the allies gain Spanish allies and bases? Olny in the case of Germany respecting the neutrality of Vichy do the allies NOT go into N africa, once the Germans occupy, or start to occupy Vichy, the allies are free to reinforce the French forces in africa. So no, once Hitler goes into Vichy, he doesn't suddenly get a 'get out of africa free pass', rather, as historically, Hitler will attact west into Vichy africa, not withdraw. The allies then have the benifit of all Spanish bases from which to support their operations, rather than having to work their war accross africa.
If you are not going into North Africa, you are better off using the forces to invade Normandy in 1943 than going into Spain.
My posts are not getting that far ahead here, where is it said that, once we commit troops to Spain, we are forever barred from using a friendly nation as a staging area to advance further? Spain might not have a world class navy, but they do have merchant shipping, do they not? And this additional shipping, and the ports within the med (as well as all the Vichy ones, after Germany invades), are going to be opened up to allied forces and operations, are they not?
You seem to be arguing that the allies would be WORSE off with Spain in the allies, is that if fact what you think and are saying? That we would gain nothing from bases, ports, and airfields in Spain, and that historically was the best POSSIBLE way to go? The only reason that we needed to go into Vichy territory was to be able to get a front going there against Italy and the axis forces in africa, and given the choice of attacking the Vichy or Spain, Vichy was the neutral that we could most easily defeat, without the German army being able to intervene other than at the end of a long, and poor, supply chain.
In this case though, the Allies do not have to invade any one. In this case, the Spanish will be welcoming allied forces, and defending against any incursion from the Germans. In this case, the ports and infrastructure of Spain is at the disposal of the allies, all at once.