The other problem is that ultra-wide band communications are much more efficient, so much so that human communications have been moving toward them for years. If you do a narrow-band search, you aren't going to find much with efficiently coded communications. That many human signals are so easily detectable is a testament to our inefficient communication technology.
I agree.
More and more we are turning to both digital cable and frequency hopping spread spectrum digital RF. It may hold true that high power RF is a very short-lived phenomena in any technological evolutionary ladder. If that is the case, SETI may be futile even if there are thousands of races right here on our doorstep.
All that said, there is another factor in this conjecture. A race is progressing along and figures out that the electromagnetic spectrum is the only real practical method of long-range communications. So high-powered transmitters are built as this technology is in its infancy. As the engineering and science of radio advances, they figure out that tight beam, spread spectrum, synthetic aperture, frequency hopping, etc. are a way of not only saving power, but also bandwidth. So for the first 50 years they have been "bleeding" EM into space across a huge range of frequencies into and ever-increasing sphere of radio noise. However, do to technological advances, this RF that is being bled into space quiets down dramatically.
Now, lets jump a few years. This race has expanded off its initial planet and is exploring the solar system it resides in. (IMHO, star travel still remains firmly in the realm of SiFi) Somehow they have to communicate. So again high power transmitters are employed to accomplish this. Light is not out of the question, however, microwave is easy, cheap, less pointing accuracy requirements, and wont be drowned out by the star. So suddenly this race again is radiating RF into the universe. So according to this scenario, a race can emit RF then grow silent for a time, and then restart emitting RF.