I went and did some low-level instances a while back, just 'cause I could. I don't group much, so I didn't get a chance to experience Deadmines and such when it was actually profitable to do so. Soloed Deadmines, Wailing Caverns, and Blackfathom Deeps. Got some stuff for a couple low level alts, but most of the stuff was vendored, auctioned, and disenchanted.
Even doing it for the quests isn't worth it. By the time you can solo an instance, all the quests are gonna be grey. If you're gonna do it, do it because you want to, and don't let anyone tell you otherwise. ;)