Your 7-speed wheels won't take 8,9 or 10-speed cassettes so to use anything with more than 7-speed STI's you would have to change either the hub or at least the freehub body, redish the rim and either cold-set the frame to 130 mm or plan on using a bit of force to make a 130 mm hub fit your 126 mm dropouts.

One possibility, if you can locate some reasonable 9-speed STI's, is the "8 of 9 on 7" technique where you use a 9-speed cassette with one cog removed. This modified cassette fits on a 7-speed freehub but requires 9-speed shifters (with one "click" locked out by the limit screw) and a 9-speed chain.

I share your trepidations about any used STI, particularly very old ones. You might be able to find a NOS set of 7-speed RSX STI's fairly cheap. These were quite good and were current through the late '90's.