In my opinion, the zeny you can make from common drops isn't that hot. (Gonryun included.)
I even did sleepers for a while, and it was niceish making several 100ks worth after a run, but for me it's lot more fun, exciting, and lucrative to get a card worth 7-12 mil after a week of farming on top of all the common drops that sell for about 200z-2kz each.
Street Minista had the right idea with the Banshees (though I guess that only works for sins
). The solo-able mobs with good rare drops are where it's at