1st of all, i dont think SETI is a waist of time or money.
i think its GREAT.... at least its a start in the right direction...
also, they use radio waves because it is a very basic form of technology.
any E.T. with the knowledge of greater technology than our own is most likely familure w. radio waves...
think of it this way...
in the 'good ol days' we made fire by rubbing stick togather to cause friction,
than we found that stricking two rock togather works better,
now we just light a match or lighter to make fire....
BUT, we still know how to make fire with sticks and stones,..,
it took a long time and alot of human effort to go from sticks to lighters
and so will searching for ETs...
im sure that someday we will find better ways to search from "home base"
but if u dont start, you will never finish...
and i think SETI is a good start