Bruce,

Responding to your comments:

"... it is now considered a near-certainty that there is still liquid water underneath the savagely inhospitable surfaces of today's Mars..."

Get on Google and look up "Nick Hoffman White Mars" (I'm too lazy right now to do it for you). Nick posts on this website and might comment on his own. Nick's theories on Mars are a "best fit" concerning current empirical understanding of that world. Once you understand the White Mars hypothesis, you'll realize that it is quite possible that there is no liquid water on Mars (does a have a significant ice cryosphere).

"...Astrobiology, as the single most important purpose (though certainly not the only one) for exploration of other worlds, is very far from being an overly expensive wild goose chase..."

Searching for life in other star systems through sophisticated astronomy (interferometers, etc.) is certainly a worthwhile activity and should be vigorously pursued. Searching for life on Mars is probably a wild goose chase. Europa is interesting but technically difficult to explore. I am very sceptical concerning Solar System exobiology. I must emphasize that I believe Mars should be explored because of its high potential for human colonization.

Gary