And one good algo change, and you just lost 1/5 (or more) of your income. Besides, I never said junk sites. There are plenty of solid, quality sites that only make $100 a month. Though if the junk site is making you money... Well. It is all part of diversity. 5 sites that make $2000 is a good start, but if you care to think about it before critisizing, you will see what I meant is that don't put all your eggs in one basket.
Make a few quality sites as a long term investment. Make a few junk sites for a short term money. It's kind of like investing in the stock market. There are some stocks you buy because you know you will turn them for a quick buck. There are some you know will pay off awhile down the road.