I've always used the gold foil cake circles between tiers but I always have to trim the scalloped edge so that they don't show.
What is your experience with the white circles? I imagine they get "greasy", but do they get soft or compromised in any way?
You can purchase coated white circles.
I've never used gold foil one between tiers. Coated white ones work just fine.
I use only the white cardboard circles between tiers and they hold up just fine. I don't cover them either. I use to until I read in cc forums that pros like Indydebi...etc. don't cover theirs. No need to. I do cut a piece of wax paper or freezer paper the tier size and place between the cake and the next tier to keep it from sticking to my cake.