Funny... I'm looking forward to my FAC tour, yet had (and still have) no desire to attend IOC.
And sorry, I don't buy into the belief that attending IOC makes you a "more well rounded Marine officer." I promise, as an aviator, you will understand the overall employment of the MAGTF and battle space far better than the average grunt will. People seem to understand the battle space below them a lot better than the one above them.
See, blanket statements are fun for everyone.
My FAC tour was the best tour of my time in the Corps, largely because we had a highly successful deployment. After wasting 8 months of my life on a MEU, actually doing something was rewarding.
Squeeze, don't underestimate what you don't know. You'll learn more about CAS from your FAC tour than from your time in the fleet thus far. I'm not talking about how to simply run a 9-line, you'll learn about the mechanics behind true combined arms and realize how much work it takes to make the MAGTF concept work. But that's also why the Marine Corps is so good at it - all the joint pubs in the world still leave the Army/AF well short of the MC in that expertise.