From what I've heard, the best money spent would be on a header and camshaft. Haven't done so myself yet, so I can not say for sure. I would say most important repair is timing chain (unless you know it was done in the last 100,000 miles), closely followed by cleaning the intake chamber of the black goo. I have just had to rebuild my engine due to trusting a bad timing chain. Keep in mind the 22RE is a great little engine, well worth working on and perf-modding. I have an '88 4Runner with one, and even with the addedrag of the front axle and the transfer case I still get over 30mpg (imperial gallons though-125% of a US gallon).
Good luck!
D'mon
