...have just made their way off the flea market for the equivalent of US $15.
Initial impressions: easily the most balanced Denon headphones for electric guitar/rock/metal/etc. Resolution is lower than AH-P372, but the AH-P372 have those awful peaks in midrange that invoke a lot of crackle and shoutiness (AH-P372 have a very irregular frequency response also, it's like a ride up and down). So overall the old AH-D210 sound is more natural/balanced, and the soundstage is larger. Modded AH-D310 outperform them of course, but the classic thing is interesting. They're also semi-open, unusually for Denon headphones which are commonly closed.
There's still that congestion, lag and dead harmonics of a stock cable. But really they outclass AH-P372, and that's all the fancier since my AH-P372 are heavily modded. Surprisingly, the foam has not decomposed (this is an old model from the 90s, if not late 80s). Aside from a few scratches and slightly faded print they don't look that bad, even.