I think the best hope for the MLS is to remake themselves as essentially a farm system for the big Euro clubs, a place to send the up-and-coming players to get seasoning instead of sitting on the bench. Soccer fans in this country would much rather watch an English Premier League or La Liga game than an MLS game. So if you tie-in MLS clubs with the big boys, I think it would get much more respect. There are some MLS clubs (Real Salt Lake and Chivas USA), that already do this on some level. But how cool would it be to watch Manchester United’s up-and-comers, instead of older players trying to stretch out their careers.
The trouble is there are so many tiers in English League, that all those up-and-comers already play in minor leagues already. Same with Spain though not as deep (La Liga and La Segunda, and maybe one other tier), though I am not sure about Germany or Italy.
To be sure it would be fun to watch MLS as the minors. Like baseball, it is a fairly fun game to see in person, though neither one are fast enough for me to enjoy on a regular basis on TV.
Lots of Americans are already playing in Europe and elsewhere. Foreign teams recruit players from MLS. We need MLS to give more Americans an opportunity to play pro soccer. In many ways it is a developmental league. Europe used to [and still does I believe] do something similar with basketball allowing only so many foreign players [non-European] to play on a team. European basketball benefitted as a result.