I think the atmosphere in most places would be weird for a first date if it were V-day. It seems like a recipe for a bad experience at over crowded restaurants serving marginal food because the kitchen is over tasked. Not to mention service staff that is stressed out from being over worked, and possibly resentful that they have to work that night. Come to think of it even if you were in a relationship I think I'd avoid going out on V-day.
Now if you were doing something like coffee I don't see the big deal.