I was on the bus last year and couldn't afford the SxSW admission. It was still one of the best things I've ever done and many things I did and learned in the last year were enabled more or less directly by the StartupBu
Gotta say - doesn't matter if you're in or not at SXSW. Maybe for the interactive, you can't go to the panels...but there's parties..and then during music? There's so much free stuff all over the city it's insane.
Just get on the bus and take it for a ride to Austin then - the bus is one of the most intense hack events anywhere.
last year i was also on the bus. in summary - it was a blast, but let's put it this way: in big part it was thanks to the bus that i've moved out to the bay area from the midwest.