All income from adsense is proportional to the site traffic you get.Making large no of sites and spider them together is also good.But when you can make 2-4 big sites all pages togetherly spidered then it will be easy to diresct traffic.So 2-4 big sites will surely generate more revenue.....
I have seen link buyers with 300 to 400 adsense sites. They must make money with the number of links they are buying.