They are quite valuable.
9000 descendants making 3 cubic meters of gold every 5 seconds for a 10-hour shift gets you:
$9000 uw \times \frac{3 \frac{m^2}{uw}}{5 s} \times \frac{60 s}{1 min} \times \frac{60 min}{1 hr} \times \frac{10 hr}{day}$
...which is 194.4 million cubic meters per day, or, in gas mining terms, 6,865 MMSCFD. So this is somewhere around Indonesia's current gas production by volume, caveats being that it's a bit harder to move, you can't use it by burning it, and you can't release it to the stratosphere if you want to get rid of it. But it doesn't go boom or cause global warming.
Gold is $19.30 \frac{g}{cm^3}$ or $19,300 \frac{kg}{m^3}$, so this is 3.75 trillion kilograms per day or 3.75 billion (metric) tonnes of metal output. That is actually around double the global steel output for a year. True, the increased weight doesn't help very often (forklift counterweights, elevators, ballast) and more often the benefit will be half or less. Gold is, as some say, flimsier than steel. But it is still METAL.
What would you do with it? Well, if gold can make thrones and crowns, it can make office furniture and computer casings. It replaces copper wire wherever copper wire is still used, and copper pipes, even PVC. Steel fences are replaced by weaker but heavier posts of gold. Shipbuilders deplore the flimsy metal but promote its corrosion resistance. Perhaps they keep a steel framework inside it. Wherever crummy screwdrivers and unreliable bolts are sold, the "white metal" made from zinc gives way to a gold and nickel blend. (At least it doesn't just snap - you can beat it back into shape)
Rolled out into leaf, gold takes over for aluminum and even some plastics for food packaging. Cast into bricks, it makes for an attractive, durable paving stone wherever a brick road will do, though I think brick works out to be too cheap per cubic meter to take on directly.
Steel was trading at \$711/tonne in a random web hit. Suppose gold is only worth a tenth of that, seven pennies per kilogram, taking on PVC and plastics and even upscale paving bricks. So that's $\frac{711}{10} \times 3752$ million tonnes daily, or \$266 billion a day. Talk about the wealth of Croesus! The present total gold value is reputedly \$9 trillion (random web site), so you can surpass that in a month or so. It is a pity that the Midas mutants are too dangerous to leave running around loose ... but they contribute mightily to the gross national product right where they are.