I have periodically gone through bouts of lens buying. I got the AF-D lens shortly after the AIS because I had read various test reports and reviews concluding the much cheaper AF-D was actually slightly sharper and more contrasty/less prone to flare at smaller apertures. I've never even owned an AF body. I never observed any difference in performance between the two lenses myself, but once I had the AF-D I just kept using it.
Originally Posted by narsuitus
More recently I had the chance to try a few ZFs. I had no expectations either way, but it turned out to be a gem. I do find it to be a bit sharper around the edges/corners in 8x10" prints. So sensibly or not, I bought it, and it is one of my favourites.
All this to say, yeah in the end it never really made much sense for me to not use the AIS lens, and to keep buying more lenses. But occasionally I can't help myself even though I know better. As John Sexton says about photographers, "we like stuff".