Is even Buddhahood itself a short straw next to material wealth and pleasure and fame?

Well the traditional story is that the Buddha was born as a Prince -- and became dissatisfied and left after meeting the "divine messengers" (devaduta).

There are three (sickness, old age, and death) in the introduction to the Jhakata, five in the Devaduta sutta:

The five divine messengers to whom King Yama draws the culprit’s attention are a baby lying in its excrement, an old person, a sick person, a robber caught and punished for his deeds, and a dead person. These are five "divine messengers" in the sense that they exemplify the inevitability of birth, old age, disease, karmic retribution and death.

I think we're meant to understand that a Prince doesn't have "unparalleled wealth and power" -- against death, for example.

See also the description of dukkha in the First Noble Truth.

And if altruism is a motive (which we're told it is), it seems to me that the Buddha as a teacher has done more good -- brought more cessation-of-dukkha -- for more people (throughout history) than any temporal monarch.

Not just complete enlightenment. The Buddha taught that even the fruit of stream entry (the first stage of enlightenment, incomplete) exceeds sole dominion over the Earth and lordship over all worlds.

From Dhammapada 178:

Sole dominion over the earth,
going to heaven,
lordship over all worlds:
the fruit of stream-entry
excels them.

The commentary for this verse:

The Story of Kala, son of Anathapindika

While residing at the Jetavana monastery, the Buddha uttered Verse (178) of this book, with reference to Kala, son of Anathapindika, the well renowned rich man of Savatthi.

Kala, son of Anathapindika, always kept away whenever the Buddha and his company of bhikkhus came to their house. Anathapindika was afraid that if his son kept on behaving in this way, he would be reborn in one of the lower worlds (apayas). So, he enticed his son with the promise of money. He promised to give one hundred if the youth consented to go to the monastery and keep sabbath for one day. So, the youth went to the monastery and returned home early the next day, without listening to any religious discourses. His father offered him rice gruel, but instead of taking his food, he first demanded to have the money.

The next day, the father said to his son, "My son, if you learn a stanza of the Text from the Buddha I will give you one thousand on your return." So, Kala went to the monastery again, and told the Buddha that he wanted to learn something. The Buddha gave him a short stanza to learn by heart; at the same time he willed that the youth would not be able to memorize it. Thus, the youth had to repeat a single stanza many times, but because he had to repeat it so many times, in the end, he came to perceive the full meaning of the Dhamma and attained Sotapatti Fruition.

Early on the next morning, he followed the Buddha and the bhikkhus to his own house. But on that day, he was silently wishing, "I wish my father would not give me the one thousand in the presence of the Buddha. I do not wish the Buddha to know that I kept the sabbath just for the sake of money." His father offered rice gruel to the Buddha and the bhikkhus, and also to him. Then, his father brought one thousand, and told Kala to take the money but surprisingly he refused. His father pressed him to take it, but he still refused. Then, Anathapindika said to the Buddha, "Venerable Sir, my son is quite changed; he now behaves in a very pleasant manner." Then he related to the Buddha how he had enticed the youth with money to go to the monastery and keep sabbath and to learn some religious texts. To him the Buddha replied, "Anathapindika! Today, your son has attained Sotapatti Fruition, which is much better than the riches of the Universal Monarch or that of the devas or that of the brahmas."

Then the Buddha spoke in verse as follows:
Verse 178: Far better than sovereignty over the earth, or far better than going to the abodes of the devas, or far better than ruling supreme over the entire universe, is (the attainment of) Sotapatti Fruition.