This kind of work has been my primary income for the last 4 years or so. Nowhere near on the same level as Feynman, but I know enough about enough other things that I get a lot of reputational referrals.
sometimes (i'd argue often, actually), you don't even need that. simply having an outside/fresh perspective and the fact that you aren't part of any of the existing groups/silos is valuable.
Having the ideas is easy. Persuading and organization to change is not.
Perhaps it’s a cultural difference between the middle of the 20th century and now.
You can be all over the ball park and people always get their money's worth :)
If you do it where the client can take it to the bank, they will often come back to see what happens with those kind of returns if they actually invest something substantial.
Ergo...