"I suspect that a lot of the core SEO knowledge is as valid today as it was back then."
Mostly yes, title tag, header tags and overall content are the main focus.
" I wonder whether there have been any particularly ground-shaking changes to the way one does SEO over that time? In those days, meta keywords were ignored,"
Meta description and keywords are regaining importance. Google uses the meta descrition to describe your site, no tag? It takes the first snippet it "thinks" is content.
The most "ground shaking" thing lately is the avoidance of the duplicate content filter. Not so much a penalty, but as a filter you can be filtered out, not just with doorway pages, but with dynamic page problems (like with phpbb, that's one tough nut to crack to avoid page dups)
"PageRank didn't count for much"
Still true, but we all like to see the green anyway, quite proud of one of my PR7 sites. Though I have some PR4 and 5s that beat it to smitherines in the serps go figga...
Don't know about java or flash, I don't use it, kinda old school page writer here. Been doing this since 1994 (most people didn't know what the word internet meant then). I don't believe anchor text is king anymore, content is, and there is a fine line between optimised and over-seo.
"SEO was still considered a black art and not many people outside the niche community even knew what it meant."
SEO is common as dirt and fast becoming a household word. And it is not considered a black art. Google even has tools to help you now.
"Splash entry pages were common and hidden text and other unscrupulous tactics could get you banned from Google."
Still true. Try it and your committing googlecide.
"Am I still in the right ballpark or have I got to start from the beginning again?"
No, your fine, just focus on content, avoid duplicate content, don't copy other folks, or even your own websites content and you will do well.
"PS hello to all the old stagers - hope you're continuing to derive success from the black arts! "
Well if you mean black hat seo when you say black arts I am far from wishing them success...
Good luck to you.