What brand? Canon's new 7D Mk2 is looking pretty sweet.
I just upgraded to the 7Dmk2 this past summer - love this camera. The 7Dmk2 is great for action photography. The autofocus and continuous shot mode are top notch - which is why I bought the camera, having active kids. For still photography (landscape / portrait) there may be better choices (in terms of absolute performance and / or value).
If you're shopping Canon or Nikon, check out www.kenrockwell.com
if you haven't yet. He's got great information - and gives great real world reviews.
This is a tough choice. Both camera and tires will get a lot of use, and are highly personal choices.
Edit: I also recommend B&H Photography if your shopping for any photo needs. I've purchased a few lenses, my last body, and several accessories there. Always get great service and great prices.
Speaking to a point made above - why do you want to upgrade the camera body? Better MP won't necessarily yield better photos (which I'm assuming you know based on your comment re: having "all the glass you want"). Better ergos, autofocus, "brains" (aka processor), low light performance, etc are typically the reason for upgrading. Answering this question might help your decision making.
If "new and shiny" is the upgrade reason, I'd lean towards new tires personally. Any technical reason to upgrade the camera, is exactly that, and I personally would lean that direction over tires that are still serviceable.