Didn't realise there were audio sync issues, but then I have my setup running as you describe so can set the delay exactly. I don't recall actually ever changing it mind, but then that's the same when I fire up Rockband too.
You sound about the same level as me really, in that I can pretty much play any chord progression but have never been much of a soloist, which is why I wanted it as I thought it would help. It can to some extent I think, but there's times when it either throws far too much at you and it's hard to read what's on the screen. If it had the ability to adjust the speed on the fly using a controller then it would be perfect, so if RS14 has that then I might well give it a go.
I tried it with my bass the other day, and it's really good for that, but that's probably because you're dealing with less info on the screen at once.