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I think history is a factor, but not a major factor. Typically when I begin a new adgroup I bid a higher cpc to get good impression/ctr numbers and slow off later on as it seems that adwords will embrase your adgroup better than not doing it..

If none of these pages are indexed, you can block them via robots.txt. But if someone else links to a search page from somewhere on the web, google might include the url in the index, and then it'll just be a blank entry, as they can't crawl the page and see not to index it, as it's blocked via robots.txt.