I've noticed from nearly the beginning of MLS that teams on top of the league tend to have little to no changes between seasons. However, I feel beginning with the 2011 season that may chang. It has long been seen in Europe that when you're on top you still need to bring in fresh players and add to the talent already in place. Barcelona for example has been a fantastic team for the past several years. But every season we see fresh players brought in to replace aging stars or to just replace players (Theirry Henry) that are excess to requirments.
I think MLS are starting to go this way, finally. MLS is a league that it is incredibly hard to stay on top of with the drafts and ways new talent can be acquired. It seems lifespan at the top is 3-4 seasons. We've watched DC, Houston and New England all spend time at the top only to have all now missed the playoffs this past season. But rarely have these teams brought in fresh, proven MLS level talent to bolster their rosters. Columbus is a prime example as they continued to use the same players following their MLS Cup win in 2008 and only slightly altering the team, and not for the better. Last offseason, Seattle didn't add to their Open Cup winning team, and paid for it this season. Blame Freddie Ljunberg all you want, but until they brought in Blaise N'Kofu the team was practically stuttering.
MLS still relies to heavily on the MLS draft in my opinion. I'm not the biggest fan of college soccer, though gems are found each season. Players aren't being developed, and it's hard to develope when you're played in a system that is continually played by that college program. But even many of the highest touted players end up on the junk heap (Chance Myers anyone?). With the redesigned reserve league hopefully more players will come through now. We've seen several teams using their academies lately, and hopefully over time that will become a bigger than the college superdraft. Hopefully, with some of the new rules in place we'll see teams adding more quality to winning systems and I believe the league needs a team that is on top or near the top every season. A New York Yankees of sorts will benefit this league in marketing, name recognition and it will give those US based MLS fence sitters someone to cheer for or hate.