I've e-mailed some whom I've already met, but I guess I've always approached it as I would speaking to investors, that cold pitches don't work. And I wonder what would happen if all 1600 applicants did the same.
I think you're right about investors and wrong about YC founders. Put yourself in a YC founder's shoes. If you got a cold pitch from an applicant, would you respond?
(note: I get emails every application season and always reply...)