There would be fans who can't see the justification of paying $55 or more just to pay $1.50+tax for a foot-long hotdog and a soda or around $3-4 for a slice of pizza and a soda. Besides, most fans would want to drink beer at the game, and it's usually more expensive.
Costco does sell beer and alcohol. I just recalled the two things I was eating at the time I wrote it. Pizza and hotdogs at Costco are reasonably priced and don't have strict regulations for supplying and serving alcohol.
The justification of paying $55 for a membership is evident when you have a family of 4 and it costs $7-9 for a hotdog, slice of Pizza, or soda. Beers were $11-16 the last time I went to a hockey game and those were 16oz beers.
The idea is essentially to make someone pay the membership fee and then let them mend their buyers remorse by consuming more (at the game/at the store) and thus seeing their savings. More seats filled, more cheap hotdogs sold.
Now, if Costco were to sponsor or partner with the local sports team, and perhaps pay for a new stadium, they could maybe offer discount ticket packages to members, and that might be more acceptable.
I could see that for sure. Keep in mind, partnering with a local team in a sport not widely affiliated with say the NFL, Costco may have the opportunity to get a manufacturer to make and sell the apparel for the team.
This could be an additional revenue stream at the games as well.
Ultimately, I think the problem with many Arenas and Stadiums is that people come in with a set amount of money they are spending at the event. If they go over that they are less willing to return due to buyers remorse. When you allow someone to chose to spend up an amount of money they have predetermined at an event and get more value for their money and all you are really doing is facilitating a few more hotdogs and a few more beers and a few items of apparel, all you are doing is exactly what the stores are doing, buying and selling in bulk.
I do think this wouldn't work for a very large sports team, possibly in a smaller sport and/or sport with fewer regulations and many teams in the league. Maybe a AAA baseball team where filling seats is just as important as selling concessions.