It seems they could come in handy to support some coins that may have value but not enough support? There are
a lot on eBay now under $100.
Definition of profitable: like earning interest on a CD/Money Market with a good amount of capital, not "day job" work,
and liking the heat (in Seattle one often uses a heater even 8 months out of the year at times).
I think it's pretty certain that you'll always have to look at the price and the power draw per Mh.
IMHO, i think that if you buy a very old, outdated scrypt miner that draws way to much power per generated hash and costs proportionally more per unit of hashrate than a new miner, you'll always do a bad deal buying one.