Is there an upper limit on the amount of money you can spend in Nintendo Badge Arcade?
Well, considering I've managed to purchase well over $100 USD worth of tokens, it doesn't seem like there is a limit. The amount spent far exceeds the amount I spent on Pokemon Rumble World (which was ~$32 USD), tt exceeds the cost of a typical 3DS game (~$40 USD), and exceeds the cost of a typical console game (~$50-$60 USD) and beyond.
It looks like there's no end to it at this moment.
I would hope that if they did stop introducing new badges and someone managed to collect all of them, they would be free to play whenever they chose. But we won't know that now, at least until the time comes. Hopefully there'll be some incentive when the NX inevitably comes and more official Nintendo mobiles games get released.