The rate of improvement of quality in MLS is directly proportional to the $$. Right now they're keeping the purse strings tight (salary cap,
"Beckham Rule", etc) to ensure league survival. I can live with that, knowing it will be a feeder league for the time being. But what's not seen by many abroad is that the MLS clubs are now investing heavily in youth academies to capture potential talent at a much younger age (the US College system is crap).
There will be a brief bump in MLS attendance after the cup and then probably back to the status quo. The casual fan will go back to NFL in a few weeks (once camps open). However, thanks to NBC, we get every BPL match on TV now. Every MLS match is televised (though most are regional), and we're seeing more and more 'soccer bars' pop up that will open early on weekends to show the matches.
Lots to be hopeful for, but still a long ways to go. I'm 50 years old and had to wait till I was 26 to even see the USA in a world cup. This is now 7 consecutive cups we've been in and 4th trip to the knockouts. I really can't complain given what it was like before...