^Well I think the touch strip was switched from analog to digital so it's more responsive. Other than that the neck is largely the same. The body is the same as well, but the strum bar is better. It's rubberized, doesn't slip, and doesn't flex like the GH:WT version. Also they use a different type of switch to detect strums. Personally I don't prefer their feel, but they're still pretty good, and apparently they are far less likely to fail over time.
It's probably not much of an upgrade if you don't play a lot on expert difficulty. Those charts abuse plastic instruments pretty badly.
Also, the GH controllers are definitely thicker necked than the RB strats, but I'm surprised that they're big enough to cause you problems.