I love these early episodes where the supporting cast get a fairer share of development. Uhura and Sulu are especially fun in the first half dozen episodes and Rand really sparkles in the Man Trap.
I think the Enemy Within was re-edited so that they could go into an Ad break on a cliff-hanger and the original episode order makes more sense in terms of Spock's conclusions.
I also believe that Roddenberry's original concept for Rand was that she would have a fairly close friendship with Spock, which might have made his teasing of Janice slightly less creepy in the Enemy Within.
If you don't give the Balance of Terror 5/5, I will hurt you.
And as for Vina, she's up there with Ripley, Leia, and Sarah Connor as one of my all-time favourite sci-fi heroines. For a sixties heroine I thought she was especially exceptional.