Yes, the jargon file and this article are mired in specifics that are probably bad. I also don't think the weirdness the jargon file gets into near the end regarding personality archetypes is very valid, interesting or useful, and it has always felt a little creepy to me. But I would say the core principles mentioned at the top of this article are pretty valid:
1. The world is full of fascinating problems waiting to be solved.
2. No problem should ever have to be solved twice.
3. Boredom and drudgery are evil.
4. Freedom is good.
5. Attitude is no substitute for competence.
That seems to capture the hacker spirit pretty well.
One problem with these 5 "core principles" is that they apply just as well to tax accounting. It's the places where ESR writes things that don't apply to contracts law or mechanical engineering where he goes off the rails, which is a telling problem with the essay.
Even more, I would say that several of the later points are very much valid still too. I'm still one of those people that believe that hacking does in fact relate to computers and electronics (!), so I think that learning to program, knowing HTML, being fluent in Unix and the ways of contributing mentioned in the article are still perfectly relevant as of today.
I do agree with jwise0, though, in that the phrasing and some details are way too specific to the author's own experience.
1. The world is full of fascinating problems waiting to be solved.
2. No problem should ever have to be solved twice.
3. Boredom and drudgery are evil.
4. Freedom is good.
5. Attitude is no substitute for competence.
That seems to capture the hacker spirit pretty well.