Ian your observation of the falling prices of used Rolleiflexes is different than mine from watching ebay. You must be referring to a different used market, perhaps used camera shops or something? The prices of used Rolleis continues to rise on ebay and is up significantly from 4 or 5 years ago.
Ari, I have a sparkling new Rollei FX as well as a very late 2.8 F with Xenotar. In some ways the older Rollei is actually better and it might be an option to consider that you could buy the newest nicest old Rollei like mine from 1980 and have it completely overhauled for less money than buyin g a new FX.
What you will lose by going with a new camera is 220 capability, self timer, focusing sports finder on the WLF and auto film loading.
What you gain by going with the new camera is HFT coated Planar (which is slightly better, especially wide open and certainly less flare prone), through the lens meter system (actually meters off the focusing screen) and much easier focus (it takes much less physical effort to turn the focus knob).
The difference between the 1980 Xenotar with single coating and the 2008 HFT Zeiss Planar is so slight as to be hardly mentionable. Also the shutter release button on the FX is slightly less smooth partly due to it's turning on the meter half way down. It isn't bad but the F shutter release is amazingly smooth and easy and the old F shutter is about half as loud as the new FX shutter, though even at that it is pretty quiet.
The cheapest prices I have seen on new FXs are on ebay from Hong Kong. There is a place in Europe called Arsenal that carries new and used Rolleis.
http://www.arsenal-photo.com/