I'm thinking of rolling three changes into my IsoMod that would make gold more important.
First, the "money" technologies will add in the ability to earn
some interest on a stockpile of gold. Each technology will grant a boost to the max interest per turn, with a rate tweaked to encourage you to have a stockpile of about 0.5 to 2.0 of a current technology in cash at any time. This eases trade, because the AI will have a stockpile of cash to buy/sell with.
Second, a cute transformation of the economy so that you have to spend cash to fund science and culture. Boost incoming commerce by 2, then charge 1 gold for every science and culture point produced. "Instant tech", such as from a great person, and instant culture does not have this cost. (buildings that generate culture will produce X culture X commerce, so building culture won't bankrupt you...)
The value of gold itself is then halved as far as the game and AI is concerned -- rushing with gold costs twice as much, maps are worth twice as much, and technologies are worth twice as much.
Third, make culture useful for more than just borders. Every 10 culture per turn produces 1 hammer per turn when building city improvements, and every 30 culture per turn produces 1 hammer when building units. Note that the culture produced costs you gold -- so this can be viewed as a form of slow cash-rushing.
Would that make gold useful enough?