Oh, no watch out for the Old Trek Cult!! Don't get suckered into spending $2,000 for a 30 year old, 30 pound bike.
I'm just joking of course-- there's nothing wrong with older Treks, riding them, or spending obsene amounts on them. They are good bikes, part of American culture and part of lost youth for some of us. I love old Treks.
But honestly, a shiny new 520 is better bike, often cheaper in the long run. But if you want to go vintage, don't let that stop you. Have fun. Old bikes are full of joy.
I'm a fan of lugged steel, but there's noth wrong with welded steel. The current Trek 520 is a really nice bike for the money. The frame isn't as pretty, but it's a lot stiffer than the older ones.
And $2000 isn't much for a classic bike rebuild-- it can be done cheaper of course, these projects always cost a lot more than you think (ask my wife)
Depending on the model, if I was holding an old Trek touring frame, I'd hold out of $400.... so I could buy a new Surly frame. I've had a lot of heart break with old frames-- it can be a kind of crap shoot.
I like my old trek (a 1984 Trek 720). I paid $300 for mine when I bought it from the original owner a few years ago. All Ihad to do was air up the tires.
Then just because I could I upgraded it into my current commuter with an internal hub. Still thinking about taking it on a tour with the internal hub set up, but I would change out the rear baskets for panniers.