I'm on my second strat, the replacement seems to work very well.
I haven't used a GH guitar before, but I can see where the tactile feedback and sound of the strum would help vs the soft strum the strat uses. I think a perfect guitar would be the strat's fretboard and the strum of a GH guitar.
I'll probably pick up GH III with the Les Paul and the GH II disc I'm enjoying Rock Band so much. It's going to suck playing some of those songs and not being able to sing/drum though. GH IV needs to have drums and singing as well, if they are going to split songs it will be bullshit if I can't sing G N R songs.