I wouldn't say that buzz dies in the offseason at all in a real sports town. and MLS is getting pretty legit these days... stadiums are packing in more than a basketball team, and are filling a void in towns without MLB - especially. Cities in turn are itching to get a club in town, and build a stadium. New York even just announced a new team, and they don't even have a stadium in the works yet. That's how juiced people are for the beautiful game these days...
Portland has Basketball and soccer. As soon as basketball is over, soccer starts up. As soon as soccer ends, basketball starts up. Those fans sell out both and are fucking APESHIT over both, more than any city I've ever seen. You see timbers news in the middle of February. You see Blazers news in the middle of August. It's crazy.
You want to go one higher, look at Seattle. No championships for any of their current teams... they still get a good crowd at Mariners games - who are abysmal, they still sell out Seahawks games, they get 38k+ out to sounders matches, and before they shipped out the Sonics, they were pretty rabid about that too.
Get them a winter sport like NHL or NBA, and they'd oversell everything all year round.
Maybe it's because it's too rainy or something, but I firmly believe the PNW fans are the best...