Hi Mark,
Along with DavidK, Son, Victor and others, I am one of the happy campers with a Contax 645. It is a mistake to fear buying/re-buying into this system just because it is no longer being manufactured. The manufacturing quantities were huge, and availability of parts or repair is not really an issue. I have experimented with all of the MF systems, including the Hasselblad H/V, Rollei 6008, X-Act and Hy6, Mamiya 645AFD/II, RB/RZ, Pentax 67, and Alpa TC. While all of these systems have their merits, I found the Contax 645 to cover almost all situations. In fact, the only real weakness (which is true for most other systems as well) is for wide angle under 40mm, in which either the Alpa or a camera with movements will give better results (... but I guess you went down that path already).
Actually, I am writing a series of articles on just how powerful this system really is, especially in comparison to the "newer" MF camera entries. Here are just a few of the reasons why I stick with the Contax system, and which other alternative systems have not been able to improve upon:
1) Unsurpassed portrait lenses (with Hasselblad V adapter). For portrait work, the IQ from the Hasselblad FE 110/2 and FE 300/2.8 lenses are unsurpassed by anyone. Rollei has a version of the 110/2, but it is huge to accommodate a leaf shutter (and leaf shutter lenses will have a limited future...more on that later). Ironically, the Hasselblad H cameras are unable to use these lenses.
2) Unsurpassed mirror damping. Although the Mamiya 645 can accept the Hasselblad FE lenses as well, its damping mechanism is absolutely horrible. Even the newest Hy6/AFi camera is nowhere near that of the Contax 645 in terms of vibration damping. The Contax 645 can be hand held with high resolution down to 1/15 before seeing any blur in 8x10 print, which is impossible with the other cameras. Of course, I guess this depends on how much coffee you drink. For me, the Contax 645 is like having a MF camera with Image Stabilization.
3) In-camera TTL flash meter. This is probably the least known advantage of the Contax 645. This produces "spot" on flash results, every time, with any lens.
4) Unsurpassed macro performance (APO 120). For genuine macro, 1:2 or smaller, the Contax APO 120 is the finest lens for use without bellows. However, this lens does flare at larger scales (like ALL other such lenses).
5) TTL Ring Flash (compact and affordable). The Sunpak DX-12R supports the Contax 645 in TTL mode for all lenses up to 77mm filter size. This is an incredible tool for the 120 macro and even lenses like the Hassy 110. There is no other portable and inexpensive TTL ring flash option for the other MF cameras.
6) Unsurpassed AF Zoom lens (45-90). The focal length range is just right, size and weight just right, etc. The IQ from this lens is same or better than primes. In fact, at 70mm (where distortion is basically non-existent), few primes can compete with it (see MTF charts). And, at 90mm, you can get 1:4 macro as well.
7) Tilt/Shift options. For cityscapes and general perspective control, the Hasselblad 40 CFE IF + PC-Mutar so far has yielded the best IQ. I am not an architectural photographer, so this suits most of my landscape/cityscape needs. (An interesting side effect of this setup is for close range, where the 40 IF lens uses floating elements to correct distortion; the PC-Mutar can be used at this close range and its shifting ability to stitch images.) If you need to go wider, or need more perspective control, then you need to go to LF...which does not seem to be your cup of tea, via your experience with the Rollei X-Act. From what I hear, you would be much happier with the Hassy 40 IF + (optional) PC-Mutar.
8) Waist level finder. I heard Hasselblad may now offer this on their H3 cameras, but this is still not an option for the Mamiya 645 cameras.
9) Vacuum Film back. When you need to use film, this option is the only one available for film flatness, to give you the best corner-corner resolution.
Regards,
David