The K-5 was my first DSLR, and it's good enough for my needs. That doesn't mean that I don't prefer the K-1 (or K-3), but the K-5 is definitely good enough. My most used camera is a GR, also with 16MP, and, yeah, it's good enough.
Would a K10D be good enough? I would say so, it's just less forgiving with exposure errors and give a bit less room for cropping --> you have to be good enough, too
I could be satisfied with a K-5 as my only camera. Some of my fondest photographic memories were recorded with the K-5.