Well, after thinking about the Pentax 645 since I started this thread, I've settled the issue. I bought a Bronica ETR-Si kit!
I handled an original Pentax 645, and was not happy -- the viewfinder was dark (like my Spotmatic F), there was no waist-level viewfinder option, the ergonomics were not to my liking, and the flash sync speed is too slow for portrait fill-flash use. I have realised that I very much wanted those features. I have been enjoying learning more about flash (thanks to Strobist) and I prefer shooting landscapes and still life with a waist level finder. My "hit rate" goes up substantially when I use my Yashica with WLF.
So I thought about it for a long time, and watched prices slip lower and lower on all MF gear. Recently, the Bronica systems seem to have hit rock bottom. The ETR system pieces seem to sell for half the price of comparable Pentax 35mm kit, which is unbelievable. I understand that Tamron pulled the plug on Bronica, but the remaining use-value in these cameras still outstrips the selling prices by a long shot.
The Pentax 645 has fallen in price as well, but the more desirable N and NII haven't fallen as much. Which means that a reasonably cheap Pentax 645 is also a fairly old camera, everything else aside. In comparison, my ETR-Si is the latest model, introduced in 1989 and produced until quite recently.
So my new kit is:
- ETR-Si body
- 75/2.8
- 150/4
- 2 x 120 backs
- waist level finder
- prism (non metering)
- polaroid back
- speed grip (makes the Bronica handle like the Pentax, but I can remove it!)
- extra focussing screen
- matching pelican case
Sorry guys, the Pentax 645 system just didn't fit my needs.