600 became 600 Ultegra (tri-color group on that Trek) then it just became Ultegra. There is a good thread about it somewhere.
Tri-color is my favorite "vintage" group. Comparing it to a modern group is a little tricky when you start gram counting but I would say that the 600 Ultegra on that bike is every bit as good as modern Ultegra, with the exception of missing some of the "features" that have become common since that time. Specifically: 10 speed rears, STI shifters, and Hollowtech external bottom brackets. Although not identical I would say the brakes, hubs, and derailers are every bit as good as today's equipment.
Agreed on the bike. $400 is too much in that condition. Rough, dirty, mismatched wheels. Wild card carbon tubed frame. I would go maybe $200 on it.