It's been a while since I've been there but I don't remember the spread in the club lounge being particularly extensive. That being said, it's quite a decent hotel and the restaurant collection downstairs was very good for dinner when I tried it. With the hours you will be at ICN, staying at the Hyatt allows to have a relaxing break without any hassle. If you go into town, you'll basically eat dinner, sleep, have breakfast and have to go straight back to the airport.