RE: hobby vs sport
All of what's been mentioned above. Building, fixing, modifying, buying, obsessing...to me that's the hobby part. I got involved in competitive flying, so to me it's like a sport. Interesting thing though is that the competition is mostly against yourself, and a little against others.
I fly for fun too, but when I do I'm like subconsciously practicing, or just trying to fly my best all the time, however you want to look at it.
Pattern/IMAC will do wonders for your flying skills, even if you decide you don't want to get too involved in competitions.