Having come to America from Ireland I can only say that I envy the way the Americans support the MLS. At home the top teams in the League Of Ireland average 2k-3k attendances despite having "traditional" teams in areas since the early 1900's and there isn't a year goes by without a club going into administration or some kind of financial trouble. The president of the FAI is one of the highest paid football execs in Europe and his salary is circa 10x the prize money the winners of the league get and most teams end if season position payments are less than the fee they have to pay to enter at the start of the season. These problems will never change because of the old boys club style administration in the league. Then you have football "fans" who fly to Liverpool/Manchester/London every week to cheer on "their" team and not only wouldn't they go to watch their local team a few miles down the road, they deride those that do and abuse the standard of the league.
So as far as the American supporter culture goes, they can chop the trees, march to the stadiums and display their tifos and I'll take that over "traditional support" that I've seen back home.