went from a 2012 MBA to a 2014 13' rMBP - couldn't be happier. Best computer I've ever owned.
13 rMBP's are a bit underpowered compared to 15's, yes. For my needs, I prefer the small size of the 13. But I only own my computers for 2.5 years, tops (depreciation curve starts dipping sharply after that point), and dual-core for most applications outside of gaming/virtual machines is adequate. I'm in Xcode quite a bit and I prefer the battery savings w/dual core, and my compile times are pretty reasonable.
Same As.
I have a 5K iMac for anything intensive at home