I've only been to one con; Supanova in Melbourne. I was on the road, living minimally at the time. I didn't really get into the panel discussions and didn't want to pay $60 for anyone's autograph/photo.
The costumes were all really neat and I got a ton of photos, but it seemed like the only other thing was all the merch. Maybe I'd enjoy them more now that I'm settled down and have a house and can actually buy things, but at the time I was really underwhelmed.