The DuckDuckGo approach of just blacklisting a few of the larger and more egregious content farms seems like a decent band-aid. It's not a real fix, but it cuts out a large number of the bad cases, since at least for me, a handful of large content farms account for most of the times when I've accidentally clicked on a Google result and then realized "oh ugh, it's one of these sites". Spammy blogs are the other big problem, but there's no easy band-aid for that one.