I did a search for Minnesota gatherings and came across this. In essence, I'm bumping it as a call out for other Minnesota gatherings.
ConVERGEnce is the largest regional midwest Con and is well-attended by thousands. They keep increasing the price and people keep coming, including a boatload of non-Con people who attend for the parties and gawk-n-stare. I've gone the last two years and won't attend this year.
Anime Detour has a population cap and they're not willing to explode. They increase their prices a little but they still "cap out" each year. It's fabulous but I have never attended.