Who was the R series aimed at? I can't think of anyone well known who is associated with them?
Who the Leica SLR series was/is aimed at is an issue of neverending debate in some (limited) circles. It is, indeed, difficult to think of "serious" Leica R users (other than Salgado), though there are "old school" wedding and commercial shooters who use the gear. I believe, for instance, that Norbert Rosing, a wildlife photog for National Geographic is Leica R user. At trade shows Leica typically will have a display of photos by professionals who use M and R cameras.
The cameras and lenses are and always have been very expensive new. Considering that the bodies from the R4 series through the R5, including the mechanical R6/R6.2, were based on a stock Minolta design, the excessive price always seemed hard to rationalize, except that it was the only way to have a platform for the Leica R lenses, some of which are superlative.
These days, with manual focus out of favor and everything being all digital, all of the time, remarkable bargains can be had if you want to investigate the Leica R line. Plus, Canon EOS adapters (some with focus confirmation) are readily available for Leica R lenses, so it's quite easy to slap a used, $400 90mm Summicron-R on a used $50 EOS Rebel. If the Summicron doesn't rock your world, it likely can be sold for what you paid.