This isn’t even a competition, in my eyes. Beach Club all day long. First, it’s a closer walk to Epcot and you indicated that you want to go there. Second, the Boardwalk has nowhere to eat inside the resort. Walking outside to the actual boardwalk to find something to eat might not sound like that big of a deal, but just wait until you are hungry during one of Florida’s famous downpours. Third, I realize you said that you won’t be spending any time at the pool, but one close up look at Stormalong Bay and I’m willing to bet you might change your mind for a couple of hours or so. And you will be glad that you did. Fourth, as for theming, neither of these resorts really take the cake in that regard, but IMO the Boardwalk has to be one of the worst. Obviously, I’m only offering my own personal opinions here, but I have stayed at both resorts multiple times and, now that I have, I will never go back to the Boardwalk. I would be willing to wager that you will think the same thing if you give the Beach Club a try.
Anyway, no matter which you decide, I hope you have the best vacation of your life and happy anniversary in advance to the both of you!