Being seen as an "expert" in your field does positively affect your salary and giving talks is one way to help there. To what extent it helps I'm not sure. But that's not really the reason why I do it. I do it mostly because of ego. I see people tweeting about giving a talk at X convention and I feel like I should have that status.

As jrauser said, though, the more I do them the less inclination I have, as it really does negatively effect my ability to achieve other goals. And the older I get the other projects become more important to me.