Kind of surprised no one has replied to you yet. All the steel frame Trek owners must be out riding. From
www.vintage-trek.com <serial numbers> looks like the frame was built late '88-early '89. That website also has copies of sales brochures if you're interested in seeing them.

I threw out that same what's-the-value question about repairing my lame 660 frame (cracked rear dropout). A couple of guys gave me great advice - the bike probably means a lot more to you than to anyone else so spend as much as you want to and enjoy spending but don't expect to get that back if you put it up for sale. From watching the posts here I've seen there are plenty of people out there who enjoy the ride of those steel frames but seems a lot of them equally enjoy finding the real bargains on ebay and craigslist.

I've used the word 'enjoy' twice there - and I think that's what biking is to most of us, enjoyment. It isn't an investment. Way too much negative cash flow.