I think there are a couple of reasons that early Treks are overlooked by vintage collectors:
First, they built a high number of frames (plans were for 6 to 7 thousand frames in 1978 - only their third full year of operations). There was an (erroneous) assumption, I think, that if they were making so many so fast, quality must be compromised.
Second, they used some automation - tubes were precision mitered by machine, and investment cast lugs were designed to need little or no filing before or after installation. "I didn't see one hand file in the whole place" (Gary Fisher in a Bicycling Magazine article from February of 1978). They did have, according to the article, "a hand-held, air driven Dynafile turning a small belt of emery cloth." This was used to do a very minor clean-up of lugs and fork-ends after frame assembly. Each frame only took eight hours of labor.
This automation, I think, led people to think of Trek frames as more of a product than a craft. I have learned, since joining this list, that a number of highly skilled brazers worked for Trek in the early years. I do not think the general public knows this. And again, many vintage collectors want a bike that was "hand-made" from start to finish, not mitered by machine, then assembled with lugs that were not cleaned up by hand.
Personally, I think they are excellent bikes. I am very happy to have paid (just last week) "only" $280 for a complete 1979 Trek 930 built up with decent Japanese components.
To read the full Gary Fisher article which I have referenced (you will need acrobat reader) go to:
http://www.vintage-trek.com/
Duncan Granger
Lancaster, PA