I just figured to put my two cents worth in. I have two Adaptall 2 lenses (28mm f/2.5 and 70-150mm f/3.5) bought new in 1982 along with the SP 2x converter. The value point for me was the combination of build and optical quality coupled with small physical size, relatively light weight and close focus ability. The Adaptall mount was value added in that it allowed me to easily switch from my (new at the time) Ricoh XR-7 to my older Ricoh TLS while maintaining full auto-aperture on both cameras.
For years the 28mm was my favorite lens for shooting landscapes with film with the zoom being used primarily for portraits and closeups. When I bought the K10D last year, I was pleased to find that the old Tamrons worked well on the new camera. Below is a close-up shot taken with the 70-150:
Attachment 9181
A few more with the 28mm (both hand-held)
Attachment 9180 Attachment 9179
The only sour points were that the 28mm focal length was less useful to me given the K10D's crop factor and there are exposure issues with the PK Adaptall mount (similar to those with other K/M K-mount lenses).
My advice?
1) If you find an Adaptall 2 lens in reasonable condition, buy it (assuming you can get an appropriate mount...see below). The prices are usually pretty reasonable (<$35 for the 28mm for instance). The SP lenses are particularly good, but more money.
2) Get the PK/A mount if you can find one at a price you can swallow. Otherwise, settle for the PK mount and learn how to adjust your exposure compensation for larger/smaller apertures. (There is some compensation in that the PK version seems to be better made and mounts more precisely to the lens.)