“It’s not a ‘gimmick,’ it’s the jackpot. That’s what it is, no doubt; you are collecting coins like crazy in that game. It’s insane how many coins you’re going to collect; the amount of 1UPs you’re going to get are going to help you, yes, but it’s like hitting the jackpot because there’s coins everywhere. And Gold Mario is able to throw gold fireballs, which allow you to gold everything else.
There’s basically every single opportunity to get coins that you could possibly think of, and you want to get them all… there actually is purpose to collecting all those coins, and I’m not going to tell you what it is, but there’s purpose, and you want to collect as many as you can." - Nintendo of Canada's Matt Ryan
When asked if the reward for collecting enough coins was a small bonus like a star next to your player profile, Mr. Ryan responded with the following.
“I don’t think that we would tease if it didn’t actually mean something.”