Since they don't get much traction and it's not like they're pushing out proper comics or such, I don't mind them much. (Or, more like we probably can't get rid of them if we tried ewe)
They do feel out of place, and I'd rather the amount be kept low. It's just a lot easier to get an audience on Tapas vs DA or tumblr.
I am biased though, since I intend on starting a series that's meant for concept art for some upcoming comics. But I guess that's not the same as what you're addressing, since they are comic related? :'D