I think SETI's well worth it, sure more advanced aliens, or even less advanced aliens might not use EM, but what if there is more than one intelligent set of ET's, and just one other out there like to use EM. We are so late on the cosmic scene that IF there is other intelligent life, then we might just pick up on it.
But as discussed, even if SETI finds nothing, it might just help refine some technology somewhere.
And even if we get nothing out of it ever, I feel it is worth it. Humans make works of art, we write poetry, we make music, for no reason other than that we find them pretty, we imagine impossible worlds where dragons cast spells and elves shoot arrows, and we point EM collectors at the sky and listen, hoping..........