Maybe there's still... something sacred out there. I surely wouldn't paint over it.
Meh, who am I kidding... I give it a week, tops. :-/
EDIT: It also never fails to amaze me the quality of work people get from what's supposedly a store-bought spray can of paint. That's skilled airbrush quality stuff there.
Sometimes I watch trains go by to look at the graffiti. There's some good stuff on them too sometimes.