To be fair, it's not $55 for just the Villa. You also get 10x Green Jacket army (nice!) and a pretty large amount of 12hr speed ups.
Still, I do feel the building should either give more citizens or should cost less at the final tier.
In another post, TinSoldier also noted that the team is "experimenting" with ways to give more citizens temporarily/reduce citizen costs in different ways. This is likely one thing they are testing out, but I imagine we will see several more methods of adding temporary citizens in the future.