Well, for me, its something new and different to try. I'd been reading about rangefinders for a while (started off by reading Sean Reid's articles on the Luminous Landscape, then branching out) and trying to figure out what all the fuss was about. Some of my reading led me to believe that this particular emperor may be skimpily clad.
Way too much fuss about the inherently smaller and lighter nature of rangefinders (my OM-4T is about the same size as a Leica M - a little shorter, narrower through the body except for the mirror box and a deal lighter) and their higher standard of manufacture (maybe with Leicas, but they don't seem much better built than my Olympus, if any). The virtues of all-manual everything? I can do that, or not, with an MF SLR too, or I can switch off AF on an AF SLR (and with varying success can do that with a dSLR if I should want to). Quality of optics? Maybe the ability to do non-retrofocus designs, I guess, but it seems pretty marginal to me (not being much of a wide-angle shooter). Otherwise, well, people seem pretty enamoured of Leica R lenses, for example, and they seem to work on SLRs! (Non-Leica ones as well, for that matter). If you spend enough money you can get plenty of high-quality glass to suit plenty of non-RF cameras. Film vs digital - a non-issue, as others have pointed out. There are film and digital RF and non-RF cameras. (Although there are few enough digital rangefinders, and they're expensive.) The virtues of having fewer options and controls? What, so I don't feel so bad if I don't use them? Please.
No, the only two things that prompted me to look into rangefinder cameras were Sean Reid's observations on the differences when composing with a rangefinder (everything in focus in the viewfinder, exclude based on aperture - rather than the reverse with an SLR; different framing due to seeing things inside and outside the frame with RF) and Stephen Gandy's observations on the greater accuracy of RF manual focusing in certain focal length ranges (versus MF SLRs; coupled with my own difficulty manually focusing AF SLRs when I've needed to do that).
So, I've been using my RF for a week now and I've found (so far) that these observations seem to be correct, at least for me. I've seen the results from 3 rolls of film so far (with 3 more in for processing). In both the act of taking the shots and the results I've seen back, I am composing differently with the RF than I have been with SLRs. And this is not just confirming my preconceptions based on the above reading: I'm composing differently from the way I expected to be composing differently, if that makes any sense! I've also found a much higher percentage of shots focused correctly than when I've manually focused hand-held with an SLR - even when shooting an unfamiliar RF system wide open in difficult conditions.
I'm taking different shots from those (I think) I would have taken if using an SLR (MF, AF or dSLR) in similar circumstances. I've intermixed shooting in similar circumstances with the RF and my dSLR and have found that I'm "natually" taking different types of shots with the rangefinder. If nothing else, this has made me think on my photography some more, and opened me up to new ways of seeing things and doing things. That, alone, is worth the price of admission.
...Mike
P.S. Now I just have to get used to the logistics of shooting film in this day and age, which is way different from when I gave that all away for digital-only.