I spent most of February telling byte_broker in his thread that 301s from expired domains were a 2015 tactic. Then I went and spent four hundred quid finding out, because being certain without testing is exactly the thing I accuse everyone else of.
Six domains, bought over January and February, all in or adjacent to one niche, all cheap - between £40 and £110. Redirected into a site of mine, one per fortnight so I could see them separately. Single hop, no chains, redirect to the most topically relevant page rather than the homepage in four cases and to the homepage in two.
Results after between eight and sixteen weeks:
Two of them moved something. One landed on a page that went from about position 22 to position 11 over three weeks, and it's held. The other produced a smaller lift across the section rather than one page, which I'd normally call noise except it happened in the fortnight after and not before.
Four did nothing measurable at all. Not down, not up.
What I can't work out is what separates the two. The two that worked aren't the two with the strongest profiles, they aren't the most expensive, and they aren't the ones with the closest topical match on paper. If anything the best domain I bought is one of the four that did nothing.
So I was wrong that it never works, and I'm not much closer to knowing when it works. Anyone got a variable I haven't thought of?