Lucas got changed A LOT for Crusade, though. Ness also got a different final smash. Off the top of my head, the moves that are exactly the same are: ftilt dtilt somewhat fsmash fair bair uair fthrow uthrow dthrow That's just 9. :/
No. Ness's up special attacks once, disappears after contact, and if it hits you you can do one hit attacks each time you touch an opponent, but does knockback. Lucas's up special does unflinching damage, goes through an opponent, and if you hit yourself you go flying further than Ness, and will do several hits with no knockback.
Because that would lose uniqueness? If you're going to get into this so much, make a poll. "What should happen to Ness's up-b? a. Change to 4th D-Slip b. Change to other(specify) c. Don't change d. Don't care"