If you don't like stats, turn away now
I thought this was an interest read. Attempts to look statistically at the impact improving a team through adding star players vs bringing up the quality at the low end. It does so using player ratings for the MLS. Conclusion is that improving the lower quality players makes the biggest difference. There are a few flaws to the methodology - but for a high level look it's pretty solid.
http://www.brotherlygame.com/2014/2/...-and-the-union
MODS: I didn't know where to stick this. Since it uses MLS data and talks about TFC - I figured here, but move away if it's in the wrong place.