First, I would try to bring it back to factory spec. It's amazing how time and miles shave off performance, and at such a slow rate the owners aren't aware. Consider getting a baseline dyno done.

If the expense of that step doesn't drain the bank account, then you may want to consider subtle changes to the exhaust system to improve exhaust flow.

However, I have found that in 20+ year old cars, a suspension refresh results in the perception of increased performance. Not from "stoplight to stoplight" but having the confidence and feedback that allows you to corner faster.