Everybody has their limit, or should have, based on what their financial situation is. I am by no means wealthy, but have spent $100 or more on a card that most would cap at $20 or so. Sometimes, it's one that has eluded me for a long time. But many times I have refused to bid on a card, or refused to go higher, based on what my personal limit is. I've seen plenty of common cards on EBay that someone listed for thousands of dollars. That's a buyer beware situation. If someone is willing to pay whatever someone wants, who can really stop them? I'm retired. I spend my hobby $ on cards. My wife buys plenty of purses and shoes, some, pretty high end, though not super high end. I guess a '52 Mantle rookie for me is like a Birken bag for her. Neither of us owns either item. But I have some cards I've paid a decent amount for, as has she, with her items.
The guy bidding $30K on a Kaboom card might be a multi millionaire. If he can afford it, more power to him. The Goodwill story is hard to believe. I'm sure you can make a small profit reselling items like this on line, but the people who get "Antiques Roadshow" rich, are as rare as hen's teeth.
There's no intrinsic value in cardboard, but there's a lot of value in doing something you enjoy!