Take a look at getting a webber carb to replace the crappy pierburg one. The webber if set up right should give you a nice boost. Either that or the the bolt on K & N filter might be alright. I think there's a webber on ebay at the moment, might be worth a look. The cam would be a good place to start as mentioned earlier.
Strangely enough, I never really bothered doing any engine mods to my driver when I had it, but then it had done over 215,000 and had a crack in the head! Ha I can remember the tank now!!