I'm at about your level too. Medium seems to easy, and hard is, well, just too hard on some songs! It seems like a much larger skill jump then from easy to medium. Not that I'm complaining. I found that playing "hard" level bass has helped with the guitar, it's not as tricky with all the chords, but still gets you used to the extra button. I've just started this week to play the guitar on hard on Beatles. I don't fail the songs, but I can get through them. On Rock Band 2 it's another story though.
I've been playing since GH3/GHWT, progressed reasonably quickly from Easy to Medium to Hard, and am now at the level where I could play the entire Beatles game on Hard, passing every song first time I played it. But some Expert songs just confound me, e.g. I failed The End, which has a pretty difficult solo in Expert, though I can pass some other songs on Expert.
On completing guitar on Hard, I started over on bass. After the first set, I found that a bit simple, switched to Expert Bass, and that's a fair challenge now, and I'm about half-way through the Story playing bass.
Some gamers have opined that the Beatles game is relatively easy compared to the others, as you've alluded to in reference to RB2. I agree: I've also got GH: Van Halen, and it's a fair bit harder on Hard than the Beatles was on Hard.
I was in a CD shop today, and the riffs being played in the concert DVD being demoed sounded really familiar but I couldn't quite place the song. I quickly realised the concert was the new McCartney in NYC DVD, and after a while I finally recognised the riffs as being from The End, but they were jamming and ad libbing which is why it took me a while to figure it out. Having said that, prior to TB:RB, I had never heard The End before...