I think the version where you go:
a = 1
b = 2
c = 3
and add the numbers in a name, and round down to a single-digit number, is so crude it insults my sensibilities.
However, just because it makes no literal scientific sense, doesn’t mean it (or other numerological systems, including just rolling dice) can’t offer a useful contrast to what our own thoughts and entrenched ideas and habits generate. I think it can work to generate perspectives. But I don’t want to be pigeon-holed by someone over-applying it.
Oh and also, just as there can be subconscious influence on the ouija board, the subconscious can do amazing stuff with numbers without us being conscious of it. Some people’s minds won’t stop crunching numbers an relating to them in creative ways, and for some it’s subconscious, and for others it’s more conscious. So I think for at least some people, there may indeed be associations with something like even the above numerology, because there are people who have emotional and color associations with numbers, and who’s minds don’t stop going over and over numbers and patterns.