More and more, mmorpgs seem to go down that trend, Rift, ESO.. to name a couple.. I think this system rewards players who remain loyal to the game by giving them a slight advantage which in my honest opinion is a good thing. Just put a daily cap on it and keep the daily xp restricted to subscribers. An extra incentive to stay subbed.
I love knowing the fact that my character is constantly evolving without breaking the meta of the game.