Maybe we approached the game differently but I had fun with the coin gimmick. The mere fact of putting a coin tally gave me an incentive to try to catch more to compete with myself, and a lot of them fall into three categories: 1)reward for exploring 2)reward for a platforming challenge (red coins were usually like that, and there's a part in the sky of the penultimate stage of the cloud world with a few coins but I have no idea how to get there without the invincible mario, I'm enjoying the puzzle of getting there normally) 3)reward for trying to think where the devs might have put some coin "switches", places where if you stand there coins will appear nearby. It makes the game feel warmer, like a challenge to see if you can guess what the devs would think, like in the donkey kong games
I felt that the lives had two upsides to them, its sheer amount made me comfortable with trying dangerous/cool stunts to see if I could, and acted as a sort of tally of the coins I got. Where it really shines is on the coin rush mode, though
About the first paragraph, the first two aspects I enjoy on their own without the need of a reason or objective, but it's nice to get some kind of reward out of it. For the third aspect
If they actually made coins useful to get then I totally do think that the theme of coins could have worked great. But it all completely falls apart when they decided to make coins mean absolutely nothing to most sane people.
That's probably it?

I don't know, I like it when a game showcases the minds of the humans that made them, that's why I hate puzzle games with randomly generated puzzles.
Anyway, here's how you make the coin collecting a worthwhile mechanic - have a fourth star coin which you only get after collecting over a certain number of coins in a level. Problem solved.
Ahh I would have loved that, and make the coins unlock videos with hints for the secrets, kinda like nsmbwii, but less spoilery
What? The general consensus is that 4-players is nigh unplayable. I played it once, and all we accomplished was that we were laughing at how much we ended up killing each other.
Exactly why 4p platforming is the best thing to come out of nsmbwii, besides homing bullet bills. Nsmbwii's let's plays are hilarious