I also ride an old bike (1984 CR250) and I have as much fun on it as I probably would have on a brand new bike. It does everything I want it to and more. The main things I don't like about it are the exhaust system (it's stock, and needs a new one) and the rear drum brake (a real pain when removing the back wheel!). It's basically stock, except for the tires of course. The suspension and power have been adequate for my needs so far - I've jumped it about 60-65 feet and it felt fine. I'm saving for a "new" bike (about a 96-97 CR or KX 250), but I think it would be a lot of fun to race the old bike first because everybody would think I was crazy ;), and maybe I wouldn't even finish last!
Andy
Andy