Suvarnabhumi (departure exit 2 post security, before immigration exit) is so easy its not worth a visit to an io unless youre there for another reason ...
is exactly my position. As James says, make sure you get a re entry permit on leaving (I get mine at Suvarnabhumi as I leave, (1000 baht with preprepared form and photo, 1200 if they do).
You just need go be inside thailand at tour extension times.