I'm current (and slooooowly) working on upgrading a 1978 hobbit myself. i agree with jb, start off with a pipe, but also get some good reeds, the stock ones blow! treats has dual stage boyesen's that are sweet! treats used to carry a polini copycat pipe, i had great results running stock with just the pipe! check the wiki / forums for the variator modding, and if you're feeling bold / wana pull the clutch plate, swap the clutch springs. i need to get the clutch puller tool yet, cappy's 3/4" female NPT puller didn't work for me :'(
I've seen good things with the Malossi kit on express nopeds, i've got one i'm going to be putting on mine. match them ports for mmm mmm good gogo! carb upgrade is good, the stock carb is OK but not very tunable. PHBG + malossi intake seems to be the norm. TJT Variator is a fair amount bigger so more ramping room, but i guess the rear spring requires mods to make it work well in hobbit.