tedster - 4:15 am on Sep 23, 2010 (gmt 0)
If you change the content of 30,000 URLs every week but keep the URL the same, then your search traffic will usually be poorly targeted and not buy - because what they searched for is no longer there.
If you make 30,000 URLs disappear every week but put up 30,000 new URLs with new content, you will have almost no time where those URLs are findable through search for they're content. Not only that, but you'll rarely develop any legitimate backlinks.
If you hope to use search traffic as a source of revenue, then I'd re-think the entire business model. Something needs to stay stable for a longer period of time.