For what it's worth, my brother had a stock '86 IROC-Z, black w/ gold wheels/stickers, black interior, 70k miles, 350 TPI, immaculate condition (had a recent high quality paint job at the time) and sold it for $6500 in 2012.
Fun facts, '86 was the only year with an external third brake light outside of the hatch, and also had the lowest hp rating of the '85-90 IROC.