I'm very interested in '98 GTS prices, owning one myself (until recently).
Back in September, I was told that a clean, low mileage, silver (more desirable) GTS simply "did not sell in the 60's", no matter if it had stripes, etc. I was told that mid 50's would be a good price to get for a clean, low mile silver GTS back *then*.
I think $55k is a good starting point right now - but I hate to say it, I don't think you'd get that for the car in this market. Might be closer to the $50k range.