FRC I think is so fun because it usually features fast paced, back and forth games. It is very spectator friendly because it is mostly teleoperated. I would venture to say that the reason we don't have full autonomous is because a great many teams struggle with 15 seconds as it is. Now, there are definetely some teams out there that have the abillity to go that extra mile to fully autonomous. That is why there are plenty of other competitions besides FIRST out there such as:
Robosub-
http://www.auvsifoundation.org/found...tions/robosub/
IARC-
http://iarc.angel-strike.com/
RoboBoat-
http://www.auvsifoundation.org/found...ions/roboboat/
Having recently competed with my team at the Robosub competition, I can say that it is a lot of fun and definetely very challenging. The best part too is the super cheap entry fees. Robosub for example was only a mere $500 for the weeklong competition it is.