I'm just throwing out some numbers here. All stats from Imagine Resources.
D7000
Quote: We were able to eke out a bit more resolution (about 2,100 lines) in the horizontal direction with RAW files processed through Adobe Camera RAW, but not in the vertical direction.
K-5
Quote: We were able to extract more resolution (to about 2,100 lines) with RAW files processed through Adobe Camera RAW, with complete extinction extended to around 3,200 lines.
D3200 (24 MP sensor.)
Quote: Our laboratory resolution chart revealed sharp, distinct line patterns down to about 2,400 lines per picture height in the horizontal direction, and to about 2,500 lines in the vertical direction. Extinction of the pattern didn't occur until around 3,400 lines in both directions. We weren't able to do much better in terms of absolute resolution with raw files processed through Adobe Camera Raw, perhaps just slightly more in the horizontal direction (about 2,500 lines), though color moire and chromatic aberration was more evident.
Nikon D600
Quote: Our laboratory resolution chart reveals sharp, distinct line patterns down to about 2,600 lines per picture height in the horizontal dirction, and about 2,700 lines in the vertical directions in JPEGs. Complete extinction of the pattern occurs between 3,600 and 3,800 lines.
SO the D7000 and K-5 would seem to be practically identical. The D3200 and D600 are respectively 24 Mp APS-c and 24 Mp FF.
The upgrade path to 24 Mp APS-c- includes more color moire and chromatic aberration.
SO what are the advantages of the two upgrades.
Lets say for arguments purposes, that for our prints we want 100 line per inch as defined by lw/ph. With a K-5 or D7000 we have 2100/ lw/ph so we could print to 21 inches comfortably.
With a 24 MP image we can theoretically print to 23 inches.
With a D600 FF we can comfortably print to 26 inches and those images will be razor sharp.
So in the end you have to ask if you want that extra capacity. What you pay for is larger file size and more color moire and chromatic aberration. Just going to the K-5 II gets you the color moire and chromatic aberration without a bit more resolution.
So, you have to ask, what is that worth to you.
For most images un-extinguished images will still look pretty realisitc so real world you can probably print to 30 inches with your K-5 or D7000. ANd if you're printing on canvas 30 inches is still excellent.
SO the question becomes would you upgrade from 16 MP to 24 MP in APs-c to get an extra 2 inches of print size given that you will have more problems with color moire and chromatic aberration and may never realize the theoretical advantage.
Would you upgrade to a 24 Mp FF, to get an additional 5 inches in print size...21 inches to 25 inches.
My question would be, it you're not using the capacity you have in APS-c, why would you consider upgrading.
The best answer I've heard from many FF owners is, "because I can".
From where I see, before I "upgrade to a 50% larger file format (24 Mp) I need to see a little bit more than what's currently being offered. The advantages are debatable, it's not all positive, where as the negatives, larger file sizes and slower processing times in PP, are not.
Personally, I think I'll be sticking with my K-5 for quite a while. IN a year or two when I next consider an upgrade, I'll look at what's available... but I know pros still shooting with D700s (12 MP).
It's quite possible there will be many people who will never want to upgrade, for whom 16 MP is already more than enough. Again personally I can't speculate on what might happen next time around, but right now, I've looked at a lot of options and I'm happy with a K-5, at least for now.