The problem is really that Germainia in the foreseeable future, has nothing the Romans want. It has no urban centeres to speak of, it's agricultural production was poor compared to the rest of the empire, it's infrastructure is close to non-exsistant. There are no known big veins of useful ores, and the small ones are underdeveloped, the population although recently pacified, has a history of violence, and new unpacified barbarians are moving into the region all the time to start wars and plunder, the manpower pool is unreliable at best, and there is basically nothing to tax.
Any roman governor will likeley see a posting in Germania as a punishment, and it will take several Legions to garrison effectively. This only excacerbates the issue of barracks emperors during the periods of civil war that frequently plagued the Empire. Not to mention the sheer amount of resources that will be needed to make holding the place a reasonable proposition.
It is a black hole that eats money and manpower and spits out disgruntled men with armies who would march on Rome should the situation arise. I'd expect the Romans to give up on Germania after about a century or so, much the same way they did in Dacia which was both more defensible and more developed.
BTW Arminius' Confederation had none of the Tribes which plagued Rome during the 5th century, the Goths, Vandals, Huns, and Saxons are still out there, with no allegiance to rome and moving inexoribly closer to the Empire's Borders. So the Barbarian Invasions of the Western Empire are still on schedule.
Also victory in Germania will only embolden Rome, which is likely to go to war against Parthia next. War against Parthia is a fight that, historically speaking, Rome doesn't win all that often. I could see Varus, drunk on victory, marching against Parthia and shattering the Legions there. Lest we forget the Parthians were an adversary that could beat Rome consistently in a straight fight. If Rome fights Parthia next and loses, they'll have to pull men from the newly acquired Germanian Province to reconsitute the Legions, after all that's about all Germania is good for anyway. Thus you still have barbarians in the Legions.
Honestly Rome is overstreched as it is, and taking Germania will excacerbate that problem as well. In the long run, a Roman Germania is bad for the empire in a myriad of ways.