You forget two major points.
1. A successful Romney presidency will set Paul Ryan up as the defacto GOP nominee in 2020. Although Ryan's experience may be "tainted" by the realities of the executive office, I don't see him wavering his principles one iota.
2. Ryan's nomination pulled off the same feat that Palin's injection into the race in 2008 did with regard to the pre-tea party conservative base. While the GOP lost some seats in Congress, the GOP based was fired up to run on all cylinders to form the various tea party contingents, routing the dems in 2010. This time around, his nomination will probably be worth about 5 or 10 house seats 2 or 3 senate seats.
Bottom line: Firing up the Tea Party is ALWAYS a good thing for the GOP!