According to the organisers, this year's SXSW festival brought in USD315 million to the Austin economy - although that figure excludes things that take place outside the official banner of the festival. (I don't think they're just talking about the dealers here.)
It also generates getting on for USD80million worth of positive coverage about Austin:
In addition to injecting hundreds of millions of dollars into the local economy, SXSW 2014 also provided Austin with extraordinarily valuable media coverage. Since its inception, SXSW has played a critical role in helping position Austin as a place where creativity and commerce are mutually valued, nurtured, and networked.In other words, SXSW is pretty much responsible for the "well, except for Austin, I guess" rider people will add when they talk, shuddering, about What Texas Is Like.