I have already had a look
here, but I thought it would be nice to put this out for discussion without resurrecting a very dead thread.
Comparing lengths, diameters and weights of Pentax A versus M lenses in the normal and wide prime range, where they are comparable (i.e. matching focal lengths and apertures) leads me to think that there's really not much between them. The major difference is the functionality bestowed by the A contacts. Now of course this is a big thing on DSLRs, because not only do you get to control the aperture through the camera, you also get it written into the EXIF.
However, on film it is a different matter. It is most particularly a different matter when, as in my case:
1) I am probably never going to print these any bigger than 6 x 4 inches for the family album, so IQ differences between types are probably not going to show, AND
2) Given the cameras I will be using, A vs M functionality is almost irrelevant.
With regards to #2, I have an ME, a P3, a P30T coming back from repair, and an MX on the way. Of these, probably the only one that would be affected by lack of the A setting is the P3 - the MX can't use A contact information at all, the ME doesn't need it (it's full-time Av by design), and the P30T has a selectable aperture priority mode at the fast end of the shutter speed dial (almost like a shrunken K2 with better viewfinder data presentation).
So for me, it seems like there's almost nothing in it. No doubt someone who had a Super Program or an AF film body, or was exclusively shooting DSLRs with old glass, and/or who liked making BIG prints, might have a very different opinion.
It all goes to show that one's particular taste in lenses can be either greatly curtailed OR greatly broadened when the intended use and nature of the platform on which they'll be used is taken into account.
Also, as a result of reading that other thread, I am now very tempted to get Daniel Cecchi's book...
Cecchi, Daniel. Ashai Pentax and Pentax SLR 35mm Cameras 1952-1989. Hove, Sussex: Hove Foto Books, 1990.
...because I have had BBA (Book Buying Addiction) since long before I ever had an SLR camera to call my own.