"I've been wondering for a while. How is it that North Korea, an impoverished, isolated nation with no reputation for intellectual pursuits and few natural resources, has nuclear devices whereas Iran, a relatively well-off country with many international ties and a well-educated elite does not?"

Soviets had/have an interest in N Korea.

For example in Korea war, N Korea used MiGs [and there were some reports of soviet pilots in some of the MiGs].

Iran until 1979 was US ally against Soviets.

You also might recall that the Soviets wanted to give Cuba nuclear armed missiles.

"(Spare us the lecture about an evil ruler starving his people so he could get nukes for megalomaniacle purposes. Clearly money was diverted from other uses, but nukes aren't built by beaten, starving peasants.)"

The Soviets had a political and monetary interest in selling [or "giving"] nuclear technology to countries. Also one should keep in mind that a nation dealing with the soviets could steal their technology.
"Capitalist" nations spy on one another, there is zero reason to assume that communist nations would not also spy on each other. One could say the the communist doctrine *requires* that one would do this. I would love to hear the argument from the communist worldview why the Soviets did not give all their nuclear technology to their brothers in arms.

Anyways, N Korea obviously is hoping to sell it's nuclear technology/weapons to other parties- so it's a business investment. N Korea isn't going to try to sell computer parts, or washing machines, it will instead focus like any criminal enterprise on black market type stuff. And it's doubtful that N Korea purpose for having nuclear weapons to reduce the size of their army needed to defend their nation against attacks. Though imagine a claim that they kill 99.9% of the people in Seoul instead somewhere around 1/2 of them in less than a couple days has some value.

"Did Pakistan sell them everything? Was there help from somewhere else? I doubt the knowledge was home-grown."

It should kept in mind that Pakistan became a country in
1956, and it didn't have a client relationship with the Soviets.
It probably the case that N Korea sold more to Pakistan rather than the other way around. It was more likely Pakistan was the broker for N Korea [and other countries or parties]. Anyhow, according to FAS:
"Foreign Assistance

In the past, China played a major role in the development of Pakistan's nuclear infrastructure, especially when increasingly stringent export controls in western countries made it difficult for Pakistan to acquire materials and technology elsewhere. According to a 2001 Department of Defense report, China has supplied Pakistan with nuclear materials and expertise and has provided critical assistance in the construction of Pakistan's nuclear facilities."
http://www.fas.org/nuke/guide/pakistan/nuke/