Correct, if you factor in the cost of a new stadium, and how a new stadium only moves revenue from things like movies theaters and other forms of entertainment to the NFL, then Super Bowls and Final Fours do nothing for the economy. One thing you may want to take note of is that there is not a chance that there would be more than one Super Bowl. So when you consider that no new out-of-state new money comes in with a new park, except for a couple of big events like the Super Bowl and Final Four, you end up spending half a billion of public money in order to get 1 Super Bowl and probably 2 Final Fours. I guess you could throw in 5-6 NCAA regionals. The economic arguments for stadiums don't hold water.
You're not spending $500 million only for 1 Super Bowl, 2 Final Fours and 5-6 regionals, those are just the bonus events where almost all of the economic activity is from out-state people who would not be here otherwise. That doesn't mean you can disregard that a significant portion of the money spent on the Vikings would be spent outside the state of Minnesota whether by folks who are season-ticket holders from Iowa, ND and SD or by folks in MN who will spent thier Viking season ticket alottment on a vacation or something similar. The argument that every $ spent on the Vikings would simply get re-directed to Gopher tickets, theatre tickets and the Mall of America is ridiculous. Sure some would, but not that much.
Can the whole $500 million be justified? Maybe not, but a good chunk of it can. And whether you want to acknowledge it or not, there is an intangible quality of life benefit to having an NFL franchise in the state as well as a venue capable of bringing Final Fours, Super Bowls and political conventions.