I'd count that kind of low quality site as spam, and the problem is that there's a basically an infinite supply of them. The boost feature is more interesting in that the curation is at least not a never-ending task. New high quality sites that I know about don't pop up all that often!

It's still not an entirely robust feature since you'll need to do a lot of quality work to prevent mediocre results from a boosted site from shadowing better results from unboosted sites, especially for users with a ton of boosts. But that quality work is much easier to justify when the manual curation is one of your core selling points and used by a large proportion of the customers vs. when it's a feature in a dusty context menu that basically none of the userbase interacts with.

> Maybe 90% of users would ignore this feature. But the 10% of power users maybe disproportionately important

I'd be shocked if the number of users for this kind of feature was anywhere near 10% of all search engine users. Something like 0.1% seems much more likely. But again, if those 0.1% really want that feature it's a great fit for a power user search engine.

It still doesn't mean that it's a feature every search engine should obviously have.