Don't forget the custom moves. Collecting them all again would just be a (greater) slog…
At least you can transfer custom characters over from the 3ds version, so worst comes to worst you can just use the 3ds version as a custom character creation sorta deal
But completing all star all over again? I'd rather just hammer it if it were actually possible (and likely it probably isn't if the 3ds version restricted it to actually doing it… so basically it won't be finished)