Well, i have a rule about not doing videos that have already been done as well as i would have wanted, because it seems pointless! The fun in editing is in coming up with what to put down, and although you may not be the most original editor in the world (you as in anyone) as long as you don't go and consciously copy someone else you get the satisfaction, but if something's already been done before, way good, especially when it's better than i could do, it would seem like a waste of time to me because that video would always just be a disappointment. (I don't exactly know where that ileia rip i did falls into this rule because i didn't think my idea was overly original compared to hers or that my editing was better or anything so let's forget that video exists!)
i have, however, seen videos where the combination rocked and i fell in love with it, but the video was done so poorly that i was more motivated to edit it than i sometimes am with original ideas[ocean breathes salty]. Video ideas that are great shouldn't be off limits because some crappy editor (or a good editor on a crappy day) decides to half ass a video cause they only did the video because they "LIKED THE SONG AND THE MUSIC

." It's more of an injustice to amv lovers and (insert musician) lovers to leave a video with one sucky version than it is to the editor who sucked with it to steal their idea.
besides, song and source combinations are such a miniscule part of what an editor really puts into his video, so it's worse to steal some kind of effect or series of clip choices or something like that than to just take the same song/source.