I very specifically mentioned potential First World outlays to Third World countries as exceptions to my point:

The other organ I was looking for was not the heart but the head. Why are some people poor, and others rich? We run on our golden treadmills faster and longer, and what do we get out of it? Something, it would seem; the indigent in America do not eat mud to feel something in their belly.

Other than that, my entire argument was based on the "happiness follows economic growth up to a certain point, then stops" argument that has been mentioned here so many times before

Happiness! A life's value is not denominated in smiles. How does satisfaction relate to economic growth?

(I also think the benefits from lack of iodine deficiency are a lot less siphon-away-able)

One day, a stranger came to the village. He carried with him a curious dried herb and sack of seed. The herb's leaves, he claimed, could be brewed into a soporific tea. Those that took it he would sleep twelve hours a day, instead of eight.

The elders again convened to consider the stranger's tea. If one man took it, that man would get less done- but if all men took it, then one man's loss would be balanced by the other's. Many in the village were fond of their dreams, they said to each other, and so the weed seemed a boon.

When they brought the tea before the village, many nodded at the wisdom of the elders, but one farmer, so poor he had to pull his plow himself, balked. "If you shorten my day," he said with despair, "then I must shorten my fields, for there are only so many days in the year one can plow, and my poor feet can only move so quickly."

A woman spoke next. "Sixteen hours of spinning buys me four fish; enough to feed myself and my three children. If I can only spin for twelve hours, then I will only get enough cloth for three fish- and which of my children would you have me not feed?"

The elders did not answer, but then one of the elder's sons spoke. "I already pay for candles to make my day longer," he said, "as the sun does not give me as many hours to read as I would like. If you shorten my day, then you shrink how large my mind may grow, for there are more books out there than a lifetime of reading, and yet I would read as many as I can."

A singer was next, her mellifluous voice carrying easily across the village square. "I enjoy my dreams as much as the next woman, but I enjoy the sound of my voice more." There were chuckles as she admitted to one of the village's many jokes. "To only sing for twelve hours a day would make me and my listeners that much poorer."

Others moved to speak, but the elders were elders because they could see which way the wind blew. "We will run this stranger and his poison weed out of our village!" they declared, and the stranger was soon running towards the woods, watched by angry eyes.

I meant it to signal that I thought the argument was correct in all of its main points, but probably falls apart because the increase in productivity would produce very small benefits rather than no benefits, and "very small benefits" multiplied by the entire economy still end out pretty huge

By 60% serious you mean you expect it is wrong? That is not how I treat my seriousness.