... Gold got too efficient in GEM; it became *better* than production.
I agree completely. On the other hand BNW right now has the exact opposite problem: You never want to spend gold on purchases because it's SO inefficient compared to every other use of gold (bribery, trading with allies, RAs, etc). In my first game of BNW vanilla I don't think I bought a single building (although I bought a trade ship and probablya worker) in the entire game.