Search engine spam is actually a fairly solvable problem if you aren't in Google's questionable position of also selling the ads that make the spam economically viable.
They can do everything except the one thing that would actually hurt the search engine spammers right in the coin purse: Penalize websites for having ads.
I don't know about that. If I recall correctly, there was a time when Google was trying to tamp down on pages with excessive advertising, so SEO spammers just switched to making pages that superficially looked like normal informational pages, but the content was all either ad copy or spun text, and all their links went to products they wanted to sell.
I get where you're coming from, but my experience is that even many people making sites for fun stick ads on the site in the hopes of getting a bit of extra cash. Lots of fansites did so in the olden days, and many useful sites, wikis and blogs do so now, especially if they either use hosting that adds them or they get enough traffic they feel they need to.
I'm not saying block ads, I'm saying prioritize sites that doesn't have ads above those that do. Prioritize those that have some over those that have a lot.
They can do everything except the one thing that would actually hurt the search engine spammers right in the coin purse: Penalize websites for having ads.