Has anyone done a side by side test with worms of the same color, poured in 1 and 2 sided molds?  If not, have you  noticed any difference in catch rate with your buddies using the other version?

I don't think the flat side matters at all.  I would say that I fish about 90% flat sided hand pours, and my catch rates have gone up drastically since I started pouring years ago.  More than likely it is a confidence thing, as is the case with using different brands of just about everything.  A lot of the time, depending on the bait, a flat side will give the bait more action.  About the only fully round bait I fish with is a stick bait like a Senko.  

No difference at all.