What sort of gain would that be for a non-world class runner? I'm unfamiliar with high level running, but I'm curious as in most sports these sort of things provide a small benefit at the top level (seems to be about a ~3% reduction in times over the past decade since the shoe wars began), and that quickly becomes statistical noise outside of the top due to diminishing returns.

But if you really want to reduce your marathon time by 15 minutes, then gaining a few minutes from better shoes, a few minutes from a high altitude training camp/holiday in Flagstaff/Dolomites, and a few minutes from a day at a gait analysis centre, may be worthwhile - or atleast a fun way to spend money on your hobby.

10% improvement on a 5 hour marathon time is more absolute seconds than on a 2.1hr marathon time.

But if you could only achieve it by adding the shoe isn't that a bit hollow?

If you are a 3:02 marathoner in normal shoes then run a 3:00 in a super shoe, you are still a 3:02 marathoner in normal shoes.