They add gold, but it is notably little. It does help, but if you're finding Smelters to not make a noticeable difference, you probably need to go a different route.
General production increases: Without resetting, the best way to get a total production increase is probably the "Solar Revolution" faith upgrade. This gives a percentage increase to nearly all production values (ivory appearing to be a noticeable exception) and, once researched, costs only faith to increase.
Another option is Paragon. If this is your first pass through the game, you're probably hitting a stall point where you just don't produce enough anything to feel like you're making any progress. At that point, you might be best served by focusing on population for a while, as many kittens as you can get, and then resetting. This gives Karma and Paragon, both of which are major boosts to production (Paragon affecting virtually all building production, and Karma increasing all kitten job production).
It's later-game, but Reactors and Magnetos give a significant boost to all production as well. Note that Magnetos give a bigger boost if you have lots of Steamworks.
Gold-specific boosts: The only way I've found so far to get more gold specifically, besides making more Smelters, is the Geodesy upgrade you mentioned.
Lots more smelters are an option, though. Smelters take only minerals (and some wood to run) to create, and Mines are relatively easy to make (and Quarries provide another option) to mass-produce smelters. If you're going to go this route, consider building a Ziggurat and sacrificing unicorns at least once, for the Tears that give another 10% boost to Happiness.
TL;DR: Smelters, Reactors, Magnetos (with Steamworks for more effect), the Solar Revolution faith upgrade, and Paragon are the best only ways to get gold before you get the Geodesy upgrade for your Geologists. Note that all of these - being percentage boosts to the Smelters' base gold production - will be more effective the more Smelters you have. To directly answer your question title, No, Smelters do not stop producing gold.