They already do that in a sense. Google's webmaster tools show you how quickly googlebot crawls your site, you can actually adjust it higher, but I'm sure their

They already do that in a sense. Google's webmaster tools show you how quickly googlebot crawls your site, you can actually adjust it higher, but I'm sure their crawl recommendation is based upon how much the algorithm thinks your site can reasonably handle. So, in theory, the faster your site responds, the more pages googlebot can crawl without crushing your servers, the more people find your site when searching, thus giving more people the opportunity to visit your site because it's fast.