A large metropolitan area is, for all intents and purposes, good for television. As a result its likely to dominate the agenda of any new potential franchise. If you're looking to fill 20,000 seats regularly however, the metropolitan area is not always the best indicator of likely attendance. It's not horrible, as it indicates a large density of people, but city metros nonetheless vary quite a lot. This discussion is in no way meant to promote or dismiss expansion options when all factors are taken into account. Rather I'm only interested to hear what people think is a reasonable catchment area in relation to the location of a stadium. You can have a place in a metro area 40 miles out from the city center and still be used in an argument about attendances. I'm not so sure that's the right way of thinking about it. Again for television this works, but purely for attendance sake it doesn't seem right to me that people living 40 miles out should be included as potential attendants. There is no doubt you may get a handful of people from these areas, but for the most part I think these aren't the people attending matches. I'm going to go as far to say that no place outside of a 15 mile radius should be considered as a potential catchment area for a club. And I would say that even 15 miles is quite generous. Using this, it radically alters quite a number of large cities, and even begins to explain some attendance discrepancies across a number of sports. Anyhow, the two part question: from the location of a stadium how far out, in all directions, do you feel people need to live within to be considered realistically as potential attendants? And using your answer in miles, how many people do you feel need to live within that radius to fill 20,000 seats? So for example, you may feel that in a 25 mile radius you may need 800,000 people to fill 20,000 seats regularly.
Here is a classic example. The Twins have had the 6th best attendance the past two years, even with a 99 loss season last year. The Vikings pretty much sell out every game (although its not much different than most NFL teams) and the Wild had 10 consecutive seasons without a non sold out game at home. The Timberwolves actually hold the record for largest season total attendance (granted it was their first year when they played in the Metrodome). The Stars get about 1,500 a game. The difference? Well one, its not a pro team and it sucks to say it but for most Minnesotans, they couldn't care less about non pro leagues other than High School Hockey / Gopher Hockey. Two, they play in a stadium that is about 20 miles outside of Minneapolis versus in either downtown Minneapolis or St. Paul. In fact, its about 40 miles from a still very populated suburban area in the south of the Twin Cities. Taking into account those two factors, it is way too far away.
IMO, the catchement area the OP is applying is too small. Rather than measuring it by miles and using 15 miles, I think more people are interested in time. I'd use 40-45 minutes of time instead. That is roughly the cutoff where people have dramatically different views on what a reasonable work commute is, so I'd think that someone willing to drive 40-45 minutes to work ever day (but not 50-55) should be willing to also drive 40-45 minutes to MLS a few times a year. This still means it is preferable for most venues to be situated in the city center, because in most medium sized metros, 80% of more of the people can get to the venue within 45 minutes. Other things metro/locational aspects that are important: -established sports entertainment (and additional entertainment $$$). In the Twin Cities' case, that would be NBA/NHL/MLB/NFL+Gopher's hockey in particular, among other sports. That's a lot of competition for a city the size of STL. -amenities around the venue. I'm more inclined to go to an event if I can walk outside of the stadium and get a beer, eat, or hang out post match than if I'm going back to parking lot to get into my car.
I don't think the metropolitan area is overrated, I think it just depends on which metropolitan area it is in question. Would FCD's attendance be higher were FCD Stadium in downtown Dallas? Richardson or Garland? Plano? Maybe, but probably not much. It really depends on the fans. That's why I think the recent expansion approach (based more on interest than the size of the market, I think) has been so successful, while some of the original teams are struggling a bit.
I think stadium location makes a huge difference. As a Red Bulls fan living in Brooklyn, traveling to Harrison, NJ on weekends may only be 15 miles away, but its practically a world away and takes over an hour to get to the stadium. I think the fact that they play in NJ definitely contributes to the fact that the Red Bulls are essentially unknown in my part of New York City
I think you're right but it has nothing to distance and everything to do with time and perception. Here in St Louis we have two team, PDL and PASL. The PDL team plays in St Charles about 20 miles and 45-60 minutes from the city center. The PASL team plays in Glen Carbon Illinois about 16 miles and 40-50 minutes away. But perhaps most importantly anyone coming from the city or south county has to cross a river to get to these games; an act which constitutes a distance as "far" for many St Louisans. While there is a real issue of travel time there is also the subconcious aspect of those teams playing "somewhere else" which will hurt the supporters connectedness to them.