Just recently, Incheon airport opened up a maglev line from the airport to a few places just nearby the airport. Right now it is free. You will see some interesting views of the airport and can see planes approaching (or departing depending on the wind). There are only 6 stops. I would give yourself an hour for a complete trip. It operates from 9 to 5 I believe. The maglev station is located above the skating ring. Its the other silver looking structure across the road. Anyhow, if you arrive and see the immigration line is moving quickly, then perhaps this might be an option.
Nevermind: I just reread your post. If you are leaving at 10:30, I would not try this. Inside the Asiana business lounge, you may be able to see some aircrafts as they are parked at the gates. No decent views of the runways however.