Khakis won't prevent many (any?) scrapes, though they will get ripped and bloody. Heavy work pants like dickies might help a bit but generally, my skin scrapes if it contacts concrete, clothed or not. I imagine it's the same for most people.

Considering bike clothing only for the aero benefit doesn't really make sense to most casual commuters, as that slight benefit doesn't outweigh the time and effort it takes to pack clothes and change at work.

...do you feel held back by or uncomfortable in your normal clothes?