To convert or not to convert resources?

That's the question. So I'm chugging away at my fantasy strategy card game, and I've run into another hiccup in the resource system. The way it plays currently is you play a resource card every turn up to 6, and that resource card can produce various resources depending on the orientation, with each orientation having a cool down before that resource can be generated again. The problem is it feels like the casting cost of cards and the card mechanics that require resources are competing for the player's attention mainly spells and creatures. I had a big problem with this with the building cards in the game.

Building cards are in a separate pile outside of the deck, and can be played as though the cards were in the player's hand. The problem with this was the creatures in a player's hand were more useful immediately than the long-term play advantages of the buildings, therefore, players would play from their hands always when given the option because resources were too scare to use them on buildings. I "fixed" this by removing the casting cost of the buildings entirely and putting them on a threshold mechanic. They can be played once you reach resource thresholds. That works and now players use the buildings as intended.

Now I am thinking of putting the spell cards on a similar system (no casting cost, but you need to unlock spell ranks), but I'm wondering if I should just make the resource cards make more resources, reduce the casting cost of all the cards (tweaking the power curve), or I was also toying with this idea to convert resources to the desired resource with gold.

There are currently three resources in the game: Tribute(creature cost), Gemstones(building upgrade cost), and Magic (spell upgrade cost). If I were to add gold (a fourth resource), it would be generated passively each turn by your building cards. This gold can then be converted into 1 of the 3 current resources in the game. This might reinforce the importance of playing buildings and not just creatures and spells from your hand, but it may also add another thing to keep track of. I looked up some other resource conversion games, and there is nothing crazy about the idea, my only concern is that it might be too much to play an empire-building game and manage a complicated economy.

So I'm curious what people's thoughts are on this. I didn't want to add more things in the game, but maybe this addition would allow players to generate the resources they want to build their kingdom the way they want to, or I should be providing the player enough of these resources in general to build what the player wants. I don;t know, people like converting resources don't they?