The reason I paid for supporter was because I really like the game and would like to support it.
Sure the extra aesthetics (jersey numbers, banners, bookmarks, scoreboards) are nice, but it's not about that. I spend more time on Buzzerbeater than I do playing on my PS3 or PC, and I used to play a lot of online games where monthly subscriptions are paid.
All being said, I like the game, and to show my support for what they're doing, I buy a yearly supporter package and plan to renew when it expires. The value, challenges and enjoyment I get out of that $40USD a year certainly justifies it.
Oh, and where's my christmas present BB????