Well, I love the idea of SETI, and it's true that if we're not listening we may miss something, but the fact remains that unless the transmitter is
very close - within about a half-dozen l.y. or so - we're not likely to hear anything, no matter how much they may want us to.
This is not simply an electrical engineering problem in search of a solution. It's fundamental physics. Bigger antenna arrays, more sensitive receivers, better algorithms, or anything else short of a repeal of nature's Laws can't improve the situation. Alas.
Still, it's a nice idea, and it's probably worth doing anyway, because who knows... Maybe some ancient probe will pass near our solar system. Or at the very least the SETI researchers may discover something of value to general astronomy and astrophysics while listening out for LGM.