So, I pulled out some Meguiars polishing compound I had left over from the days when I was hot to rub out a finish and tried a couple spots on a boat.

They looked marvelous!

Regular use just imbeds some dirt and grime in the varnish and the Meguiras shined it up without a lot of work.

Yes, polishing works especially well on older hardened finishes. (Gelcoat too, but that's a different thing...)
I tried rubbing out too-fresh varnish once - not a pretty thing.