Very interesting -- I don't look at much fanart either, so I'm equally uncertain. There are a lot of attempts to develop a vidding aesthetic, which I'd say is distinctive as compared to, say, machinima or music videos generally. I just don't know if fanart has similar stuff happening, but I'd be a bit surprised if it weren't. I expect, however, that explicit aesthetics coexist with lots of "pretty!" just as it does with fanfic and, to a somewhat lesser extent, with fanvids.