I don't think rooting the Nexus 7 voids its warranty. It has a ton of built in developer tools that are accessible only after unlocking it.
Rooting will not change the state of the device in any way that would affect the behavior of an AppGameKit app (unless of course you've written the AppGameKit app to need root access to browse the root directory). Installing a mod or flashing a new ROM might change the behavior, but I'd not recommend that and it is not needed to root the device.
You simply unlock the device and boot into a recovery ROM to install SuperUser so you can allow apps to have root access. This can be undone with less time than it took to root it.
My wife's Nexus 7 was rooted when she sent it in for replacement (the USB port broke) and they never asked a question about it.
I rooted my Kindle Fire and unrooted it (almost as easily) before I sold it. You cannot tell the difference.
I too was very cautious about rooting until I tried it a couple of times. The Nexus 7 is very root friendly because Google WANTS you to use it as a development tool (same with the other Nexus devices I've heard).
Oh course, it is still your prerogative, but as a developer you may find that it comes in extremely handy. There's a ton of benchmarking tools on the Nexus 7 that can really help out.
I imagine that you have to have it unlocked to Run APKs from Eclipse to it... otherwise I think you can still just Export the APK every time and copy it to the device to install it. But that could become very tedious in a testing environment. I do understand not doing this to a new phone though, the phone's got a sim card which they don't want anyone to access ever.
@Funnell7