I used to live in a small town called Hallgarten, next to Weisbaden (which is kind of west of Frankfurt). It's a beautiful little town, with vinyards, ancient houses, etc.. so my suggestion is to make sure you go to a few of the old back county towns... the Rein river is beautiful...
as far as parties... check out the Voov Festival ... a neo-hippy hedonist gathering of sorts, chock full of psychedelic trance... if I was in Germany now, I'd be going...
http://www.voov-experience.de/