Incidentally, if our hypothetical rule system ends up looking a lot like Civ (or anything else), is that bad? Or a legal liability?
As it is a gaming technique and not unique to the game no, it would not be any sort of copyright.
And it would be good, as long as a GM-style person tracks your food, science and production. Gold you see how much you have. The others are more numbers in the background sorta deal. You know the Barracks takes 60 production to complete and you know that city is producing maybe 17 production each turn, but you really don't want to have to track that yourself, or add up all the science being produced by all your cities and figure out how many more turns into you've researched "Super Forged Armor" or whatever. Let the guy who handles hundreds of numbers for a living do that.