I've sometimes wondered whether it would work for a search engine to reduce the indexing problem by focusing more on quality than quantity. Rather than indexing

I've sometimes wondered whether it would work for a search engine to reduce the indexing problem by focusing more on quality than quantity. Rather than indexing everything in the universe and then trying to rank it, focus on maximizing ROI and keeping the aggregate quality of the corpus up by aggressively pruning low-quality paths up-front. In practice this might require splitting the difference between classic Yahoo and modern search engines, with manual maintenance of various black/white/greylists and rules to assign different quality metrics for different users on social media sites, which might reduce the effectiveness of this approach. Anyone know if something like this has been tried?