You're right in that Belek itself is pretty pointless with very little to see or do if you're not interested in a ton of shops all selling pretty much the same shiny souvenirs, clothes and other touristy stuff.
There's an old ruin that they've turned into some sort of fountain/waterfall that's worth a visit if you're there anyway, but hardly worth the trip on its own.
There's also a decent golf shop (Golf USA) with a simulator to try out clubs and a good selection of clothes, shoes, clubs and pretty much everything else.
Belek is just a few minutes by taxi from Cornelia though, so we spent quite a few evenings at the Mambo Lounge, which imo, is the only real attraction in Belek - it's a very good one though