That's actually exactly my philosophy [1]. I agree with each of your examples (water on mars, photos of Pluto, early-universe cosmology). Nonetheless, the existence of extraterrestrial intelligence is in a completely different league. The random guys on the street will not only care about this tremendously, he will care for the same correct reasons that scientists care.

[1] Minus the part about it being a waste of taxes; just because people aren't interested doesn't mean it's not worthwhile, because people can be wrong.