Rather than try to guess what current classified information should be declassified, you can look at declassified information that see what kind of clandestine operations we ran in the past. Analyze events like the Iranian coup, the Nicaraguan coup, Bay of Pigs, mishandling of Iraq war intelligence, etc., and you realize that people running these programs aren't smarter than the average person and they need to be held accountable.
Look at Area 51 history in dax's article. How much money did we spend on spy planes (and trying to keep them secret), and for what?