There is definitely something to this, but I'm not at all clear what is best.
Here's some more anecdotal evidence.
A couple of months ago, I took out my most accurate 22 (A cheap Marlin 795 with a scope), Freshly cleaned.
3 to 5 MOA, 5-shot groups were the best I could do.
I put the gun up dirty. A few weeks later, I went shooting with my boss.
I was consistently well under 2 MOA for 5-shot groups.
After that I cleaned the gun.
Two months later, I took it out and got groups all over the place, but mostly 3 to 6 MOA.
Dad, who knew all about guns, died when I was a kid, so I'm having to teach myself in my old age.
I have always heard that a good owner kept his guns immaculately clean.
I'm still learning, but It seems like something is telling me not to keep my 22's quite so clean.