I agree with all of the above, there are pros and cons to both, not counting weight.
The difference between 16 and 24 MP isn't very much in practical use, although it does make your files that much larger, but let's do a quick rundown:
D5200 Pros: - Very slightly better low light performance. - Higher resolution. - Light weight. - Articulated display. - Better video modes. - Mounts pre-AI lenses (read: very old manual focus).
D7000 Pros: - More physical control points, including a sub command dial. - Magnesium body (D5200 is plastic). - Some weather sealing. - AF fine tuning. - Metering with manual focus lenses. - Optional battery grip. - Longer battery life. - Higher speed continuous drive. - Deeper effective buffer (smaller file size). - Dual SD card slots. - Can autofocus with all AF lenses, not just AF-S.
I have the D5100, and I'm very glad I own it, as it's a fabulously lightweight body, especially with the 35 f/1.8 on it; however I definitely feel it's lacking in certain tasks and wish I also owned a D7000. Even now that the D5200 is out in the US, and I obviously own a bunch of compatible accessories (not the least of which are power related), I'd still go with the D7000 as a second body - the weather sealing, higher build quality and extra command dial are invaluable.
That said, unless you're planning on going out and buying new glass for the D5200, your situation favors the D7000 even more than mine - you have a bunch of screw drive glass (every single one with an aperture ring, so go look at them), and the D5200 won't autofocus with them at all.