After riding the last 7 Bike New York's (with a 40,000+ mass start), BikeDC seems like a club ride.
I've never thought of rides like this as dangerous. You do get all levels of rider showing up. You just have to take it easy and ride careful. I find the "experienced" speed demons cutting through the crowds to be more a problem than the wobbly noobs.
Generally, the mass shakes itself out after a few miles and you find yourself riding with a relatively small group around you.
Hill climb??? Mass Ave??? That's a hill???