I have had good luck with my higher mileage 97. No CEL issues in the lifetime of the car. The varioram helps bring torque to the engine at lower rpm which makes it very nice to drive. It's not just about peak hp. Also, if you start with the VR, nobody says you can't hop it up and get even more power.
You definitely will want a PPI. However, there are no real common horror problems on the 993, say compared to early 964s or mid year (74-77) carreras.
Cheers, George