Sorry, I got out of the moped world... riding a Honda cb200 now...
the QT was a nice introduction to the 2 wheeled motor. I enjoyed it a lot.
THere are several posts on this message board refering to shop manuals. Im sure some one would be willing to photocopy one for you.
THe value is tough to say. I sold mine for around $160 if I rembmer right. The book value on my 1980 was around $70. Mine was in good original condition, and I had several extra parts go along with it in the sale. I have seen a few fully restored QT go for a few hundred on ebay.
The QT was made fro mthe late 70's through 1986 or so, but the motor and drive train still exist, in updated form, on the PW 50, and similar Yamaha's.... So technically parts are still availible, albeit from Yamaha, and dealers are traditionally more expensive...