If you like Idine restaurants enough to go there a lot, yes. If you value miles at 2c each and get, let's say, 6 miles per dollar on average (allowing for bonuses), then you are getting the equivalent of 12% back from the mileage program and 20% (for a $49 fee) from Idine Prime. So you need to spend around 100/(20-12) times that amount, that is $612.50 in a year, to break even. If you value miles at 1c each, only average 3 miles per dollar at Idine, and manage to get the Idine Prime for a reduced $29 fee, then you break even at $29 * 100/(20-3) = $170 / year.

On the other hand, if like me you have one credit card to keep your US account active, one to keep your UA account active, one for AA, one for CO, ... then the amounts don't matter that much - even 1 mile for the whole meal is better than any smallish cash refund!