I don't know how it changes the marketplace worldwide, but Soarer's converter makes the Model F viable with a modern computer.
F ATs have always been valuable and the going rate seems to be somewhere in the $125-150 range, more for a really nice one.
F XTs were really cheap (<$20) until a couple of years ago, when Soarer came along, now they are at least twice that. I see them on ebay listed for $100 or more, but I doubt that anybody gets that kind of money. They feel great but the layout is impossible, for me anyway.
The large 122-key F boards can be modded to a nice layout, and are getting a lot of interest lately. I love mine but only because I can get a near-ANSI layout with capacitive switches.
I can't see the appeal of the the M-122s, unless you just want extra keys and have the desk space. Otherwise, I would imagine that an M-122 should sell for 1/2 to 2/3 what a regular M sells for, and you will probably need to spend $22 for a Teensy to go with it.