I had thought to do ABS, but then someone pointed out the need for good ventalation. As it will be in a 6x10 room and the door will likely be closed while printing, ABS will be a rarity. I do want a printer that gives me the flexibility of media types though (I'll print my next IMSB!* ).
I've seen mixed reviews on multi-extruded printers. From what I can tell, unless you are spending $$$$, they aren't that reliable and/or tend to have thicker layers (basically the cheaper options are based off older tech and kinda hacked into the firmware).
There are some options out there to allow a single extruded model print multiple types, but there are mixed reviews on that as well.
As far as the used market, my biggest concern would be more how it was cared for than how many hours it had on it. If I had a bunch of experience and felt comfortable tearing into and debugging them, the discount would be worth it. As my first printer, however, I'd like to keep the WTFs to a minimum
* actually I'm thinking about trying my hand at a replica dual row complete with the spindle. Printed with a brass filament and polished up it might even look close to my real one