I think you may be being a bit naïve here. The average ticket price for the Bucks at the Fiserv Forum is $130. The court side seats are all sold out and those cost into the thousands.
Likewise the Packers don’t sell a ticket for less than $135, and they go for at least double or triple that on or even more on resale sites, where I assume it is not exclusively out of town purchasers.
So yes, if product on the field is good, the evidence is already there that plenty of local customers are willing to spend premium dollars for sports entertainment.
Of course with 81 games the Brewers will always need to have bargain seats, however like I said earlier if the Brewers can get 500 people to spend $300 each on a game, that generates more revenue than 2000 people who eat and drink their own stuff in the parking lot and buy a $45 ticket.