Yes, Virginia, there are practical applications to the Mars rovers' discoveries:
The Opportunity findings show that the strategy of "follow the water" was the right direction to pursue, said Geoff Briggs, Scientific Director of the Center for Mars Exploration at the NASA Ames Research Center at Moffett Field, California.Briggs said that the forthcoming Mars Science Laboratory mission will carry a new generation of instruments to help decipher "in the field" the history of the red planet. The prospect of a returning to Earth soil and rock specimens from Mars next decade, while sure to be scientifically rewarding, would also flex the technology muscle to eventually send humans there...Over the years, Briggs said, robotically returning samples from Mars has been inhibited by two things: high cost and high risk.
The NASA initiative that calls for humans to Mars in the foreseeable future, Briggs said, should give more programmatic support and the funds to make a robotic return sample effort happen before astronaut explorers set foot on the planet.
Granted, most are for future exploration - but pure exploration has rewarded the American public with a wealth of dividends. And if that's not enough, fine: let's spare the killjoy taxpayer and reward the private sector with full privileges to explore space. Aviation wouldn't be what it is today without free enterprise. It's win-win.