An alternative solution to the Fermi paradox would be that radio signals fade into the background fairly quickly. SETI only has the ability to pick up signals coming just few light-years away (if emitted by an Earth-like radio culture). It would be expected that a more advanced civilization would prefer to use highly focused directional beams (perhaps lasers), signals which won't (easily) get picked up by those to whom they're not intended. Even now, as communication bandwidth is increasing, it's mostly as ground-based fiber optics.
Yes or 'they' might use a form of energy that is totally foreign to us. Maybe it's not even a beam or a ray. Maybe it's micro-black-hole-oscillation (yeah, made that up). I mean, who knows? It's all hypothetical anyway. And here we are spending money on a bunch of dishes that pick up a specific range of radio frequency. Stick the same dishes on top of a sports bar and at least we can all watch football.
The advantage of SETI is that the radio equipment can be used for radio astronomy just as well. So the money spent has dual use (almost complementary).
