"And I often use his description of how and why wages rise: in the absence of both a reserve army of the unemployed and also monopsony (what he called monopoly capitalism) then wages will rise with productivity as capitalists compete for access for that scarce labour from which they make their profits. It was from this that he derived his warnings about monopoly capitalism."
I think the problem is that the two contingencies mentioned have appeared. With a broader market (access to more potential workers) and increased efficiency and automation (meaning you need fewer hands to get the job done), you end up with that reserve army of the unemployed. As for the monospony, you can get that with an oligospony as well. They conspire to milk the consumers dry and only then fight for what's left, and you end up with cartel behavior.
"Of course some of his predictions are looney tunes ....like, say, the idea that monopoly capitalism is inevitable, rather than just something to be aware of and thus avoid."
Well, unregulated, capitalism WILL eventually result in an ultimate winner: one who has all the cards and can use them as an infinite barrier of entry to block any upstarts. Think of it like a poker tournament. As players fall out, others amass lots of chips and can use them to muscle out the competition. Sure, some get unlucky, but on average the more you have the better you can fend off. And eventually, someone's going to have all the chips.