The posting fee issue isn't as clear cut a negative as some here are making it out to be. Darvish was able to pitch in MLB from the get go. Not even top 5 picks typically do that, like Hultzen, Gerrit Cole, and Bauer. I forget what the typical cost of developing a mid-rotation starter is when you consider the failiures, but I think I heard a number of $20MM. For the Nats, Strasburg aside, for every JZ, there was a Smoker, an Everts, a Balester, McGeary, and more. If you don't consider Detwiler a mid-rotation type, add his name to that mix, too.
for a team up against the luxury tax, the fact that posting fees do not count against the threshold also is a consideration. Texas is not quite there, but for the NYY, the Dodgers, and the LAA / Boston / Philly / Detroits, that is a big benefit too.