Another thing that soccer has going for it, especially in today's day and age, is that it is a 2 hr event (if that) and that's it. You get 90+ minutes of soccer, and half-time, and you're done. Whereas baseball is 3 + hours long (and not a lot of action, and this is coming from someone who used to LOVE baseball), football is 3 and a half hrs long, and the last 3 minutes of a basketball game is 3 hrs long.
With soccer, you're in and you're out, there's tons of action (if that's the type of action you like - non-scoring action), watching it on TV there aren't commercial breaks during game action, etc etc. I love going to Galaxy games (even though the soccer isn't very attractive in comparison to mis espana equipos) because the crowd is lively if you sit in the right spots, you're in and out in a decent amount of time, and you're SUPPOSED to be loud no matter where you sit (as opposed to Laker games where if you have decent seats no one says a word until the 4th quarter).
Soccer has a LOT going for it. While I don't think it will ever catch the top sports in this country, there is definitely a growing market for it in the U.S.