I believe THE biggest factor is location. Some spots will fetch $3k+ for a nice Super. Other areas simply will not. There have been beautiful looking Super's around me posted for a while now that simply aren't selling because the people are asking too much (for the area) for them. Take this guy for example:
http://rockford.craigslist.org/grd/4519994104.html
Good looking 2084, rebuilt engine, 54" Haban blade, 54" deck in great condition, plastic is intact, 150lbs of wheel weights and it's been being re-listed for a couple months. The guy wants $1950 for it. Simply put, no one wants to pay for a machine from 1993 when they can go to a box store and get a new one for the same price. The guys like me would LOVE to have that, but cannot afford it.
Same thing here:
http://lasalle.craigslist.org/grd/4471321934.html
1872 with a decent hour M18 (780hrs), metal looks in good shape, 60" Haban deck, again, in good shape, listed for $1750. Not a horrible price, but hasn't sold in over a month.
Then you have guys like this:
http://chicago.craigslist.org/nwi/grd/4491406747.html
$4150 for an 1872!?!?

No 3pt, no rear PTO, and listed scratched up hood. The good: 222 hours, front hydraulics, and a 60" deck. No blade, no blower, no plow, no tiller.
Then you've got a couple 1863's and 1864's that have been listed less than a week that have sold like hot cakes. Guy I know just picked up an 1864 with a 48" deck and over 1k hours for $600. I just got an 1863 with less than 500 hours on it and a 54" deck for $650. I've seen other ones that have sold listed for $750-$900. My points is, it seems like around here (north to central Illinois), if you have your older Cub listed for more than around $1200, unless it has toys and accessories with it, it won't sell very quickly. Rant/preech over.