Blowing up stars and such isn't going to generate a sign of intelligence unless something happens that distinguishes it from a normal stellar explosion. Maybe a nova happening to a star that is way out of the normal sequence for such things, but even there, it just may be a case of us being ignorant of some unknown physics phenomenon.

It's possible that interstellar communication happens on a level equivalent to what radio might be to a culture that normally communicates with drums. If so, it's pretty much moot until we get to that point.

I think listening in is worth the tiny amount (relatively speaking) of money spent on it, but I'd bet we're going to find out more in the short run by using space telescopes and such to examine solar systems for Earth-like planets, particularly those that might have water or oxygen.

I believe the most significant discovery in the near future is not going to be evidence of intelligent life, but just evidence of any life that has independently evolved outside of Earth (we may discover this in our own solar system).

Right now, we have only one data point: our own planet. If it can be shown that life can evolve independently ANYWHERE else, particularly under harsh conditions, it becomes obvious that, in a universe this size, life can evolve independently almost EVERYWHERE else.

We already have scientific reason to believe life can evolve under many radically different conditions, but we have no proof yet that it has actually done so outside of our own world.