The rate of player movement within the league is actually no higher than in most European leagues. However, there's a difference in the way the players move: because every club has exactly the same amount of money to spend on players, there is no "big club" that consistently has better players than the others. Note that there were 5 different clubs on top of the table within only the second half of the 2004 MLS season - that's half of the league! For the same reason there is also rarely a club that is significantly weaker than the others - last place in MLS was 33 points from 30 matches, which in most leagues is sufficient to avoid relegation.
That, of course, must the would-be-weaker clubs appreciate, but it allso means that if a team, manage to create a hype, like we have here in Malmö right now, the team would not benefit from it. This season Malmö FF had in average 20060 attendance per match, if we had had your system the increas in incom would go strait to the Swedish Football Association. Doesn't sound right to me!