While putting Lucas in Brawl was tenuous and a bit of a risk (seeing as most western audiences had no idea he even really existed by this stage), I think it was worthwhile. True that earthbound is now a bit over-represented when it comes to comparing them with characters such as C. falcon and yoshi, but really if Ness was in the first game, by smash 4 or 5 people would have started to think about the possibility of another character anyway, especially if F-Zero and yoshi reps came in by that stage. Putting in Lucas sets them up so that they don't need another rep in smash 4 but are still well represented. Indeed, the very fact that Sakurai chose to add Lucas is a tribute to how he feels about the Mother series. While some may disagree, I think Lucas has a decent shot of staying because his character was done nicely in smash and I suspect (but could be wrong) that he is popular amongst the Japanese audience.
As for Ness and Lucas movesets, tbh it doesn't bother me that they've borrowed their movesets from others. All that I want is to see their moves upgraded in smash to the point where they can actually be a good character tier list wise. To me this involves reducing lag on smashes, putting more range on attacks that need it and taking away the extra 10 frames of grab release animation, as well as some more minor stuff.
Anyway, that's my two cents.