The technology and human capabilities that seem to have been lost someewhere in our evolution.
Can you imagine how advanced we'd be if we had increased our own intelligence proportionately with time?
I won't even go into the reasons for my beliefs but this is a theory that, should it have received as much attention as biblical study, may have actually been proven right or wrong.
As for picking up space crap, we are told that it all eventually 'decompses' over time but it has caused major problems with OUR space exploration already.
Regarding manned missions, well obviously if we can't get some metal there, perhaps we're best not sending people there although, given the chance, I'd like to choose a crew or two for the trip.
Who knows, perhaps some higher intelligence (If you are humble enough to not think we are the most INTELLIGENT life form in the universe)may have even been trying to study OUR solar system and they've intercepted the signals from Mars.
They probably think we live in horrible conditions and look like Mechano toys with tracks.
We could build a manned shuttle to mars on a clean up mission and have them carry garbage bags and tongs; Saddam Hussein, Osama Bin Laden, G.W.Bush, Martha Stewart, Michael Flatley for starteres, with a second crew close behind.