I want a Zeiss Ikon.. Tell me why I shouldn't do it..
You're kidding, right?
There IS no reason not to do it.
Nobody ever found themselves lying on their deathbed with one of those little cartoon thought bubbles above their heads saying, "Damn I'm glad I didn't waste any of my money on that camera I really, really wanted. Now I can have a nicer headstone. Good on me. I'm ready to go now..."
"They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."
— Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs
A new idea I came up with last night.. I have a Nikon F100 body. I've heard amazing things about the new Voigtlander 40/2 Ultron SL II. I'm wondering how this lens would compare to the Zeiss lenses. I've seen sharpness tests where it blows away Nikon's primes, including the 50/1.8. I know it's not a RF experience but I don't mind using the F100. It's a great camera. My only concern would be focusing in low light. RF are supreme for that. Manual focusing an SLR is a bit tricky in certain situations. Thoughts?
"blow away" in the sharpness department for shooting Air Force test charts vs getting a lens that is plenty sharp enough but has the character you want can be very different. Personally I've not been very happy with most Voigtlander lenses and bought then sold a few. Sharp enough in each case, just nothing special in the character I was looking for. Totally subjective but just saying.
"Well, my photos are actually much better than they look..."
If you only use Medium Format, I think 35mm will help you in having the camera with you in more circumstances, or in having with you a larger set of lenses with the same weight.
Small range-finders in particular, such as a Leica M but also a Minolta CLE, or a Contax G1/G2 as suggested, can enter within a small bag with an entire set of lenses, let's say 21, 28, 50, 90 or 24, 35, 90 for instance. The weight and volume is going to be very small.
I would personally prefer to buy two cheaper bodies (such as Leica CL, Minolta CLE, a second-hand Zeiss-Ikon etc.) instead of just one. That would drastically reduce the number of lens-changing operations (which are always a nuisance) or allow to go round with two different kinds of films.
The advantage of the small format is that it is small. The technical quality of the picture depends much more on the lens than on the camera. Expensive cameras are OK if you have "excess money" to spend in photography. Otherwise I would concentrate the expense on the lenses, going for less expensive but quality-wise perfectly functional alternatives.