Whoa! We're literally and figuratively on the same wavelength here.
Although I'm a Rare Earth and rarer still inteligent life skeptic I find the uncertainty in our knowlege of the universe combined with the tremendous reward of a positive result to justify the effort for rational searches. Although I have in the past contributed to the planetary Soc's SETI search (just in case there WAS some low hanging fruit to be found) I believe that it is clear that OSETI is the way. Forget the 60s paradigm of radio telescope wavelengths. The massively parallel amateur search you advocate is readily possible this century given the net and the advent of automated telescopes. Paul Allen has built the receiver array for yesterday's war. Too bad.

As to should we transmit, the answer is Hell No! since I do not share nicey nice Carl Sagan 'Oprah' view of the universe. I too had realized that the impact of one relativistic spaceship is far worse than any doomsday asteroid or comet. Kenetic energy is a bitch.