Yesterday at Develop I attended a number of talks about socialised games. The advice across all of them was largely the same: make it social.
There is, however, something to consider: For social to be valuable to a player, she needs friends in the game. It is exponentially less valuable if she has few or none, and gating that requires her to involve her friends becomes a much harder task from a standing start. It's Metcalfe's Law basically, and is why social layers work for games that already have millions of users, but not for small ones.
Instead, consider connecting strangers.
If your goal is to get people playing with each other then why trap them in the silo of their friends? Are you adding friends-only social just to force players to market on your behalf, or is it a real part of the game experience?
If it's just marketing then change it: You're being selfish and creating walls that players shouldn't have to climb over. The first rule should always be to remember that it's about them, not you.