I think that 3-4 resources should be enough. I mean when you start adding different elements into the game as resources, we'll eventually end up adding the entire periodic table.
Although 1 resource I would like to see is some facility that actually makes ship crews(for those not using Master Computers). I think it would be cool to have to build academies where it turns out a standard amount of graduates or it's based on population size. That way you would have to make a balance between the number of ships you build and how many people are actually part of the navy.
So everytime a new ship is built, the amount of crew needed for the ship would be deducted from the 'pool' of crew. And if you build too fast, and you don't have enough crewmen, then you're ships aren't going anywhere, which I think would happen in real life. (Imagine asking a ship to depart without its captain, only 1 engineer, 1 chef, and only a couple of red shirts
. That just wouldn't happen...would it?)