If you're looking for a nice car with performance potential, and something that's easily/affordably "modifiable", I'd consider a Volvo turbo. They're rear wheel drive, and less "quirky" than Saabs. It's a very straight forward car to work on. I think you'd probably even find it easier to work on than your 240D.
The stock output of a Volvo Turbo is 165hp (and I believe 195 ft/lbs of torque). Which makes it a nice snappy ride. (I have a 940 Turbo, and it's really quick off the line.) You'd probably dispense of most lower-end imports with that kind of power.
But check out this site:
The info provided there can get you into the 200hp range with an alarmingly small investment in time and money. If you want to get more serious, you can reach the 300+hp range pretty easily too. With that kind of power, and some reasonable suspension upgrades, I think you'd be able to run with just about anybody. And for pretty cheap, I might add.
Those punks driving daddy's car will be left wondering what hit them.