I don't really see the Spendor D series sitting comfortably with the Harbeth or Classic Spendor speakers. The D series floor standing speakers are, to my ears, "Spendors" in name only: otherwise they are simply modern speakers and sound like it. I don't find any particular continuity from their classic sound, no particular "Spendor magic" in the mids that sounds like Spendor. Which doesn't mean someone can't like their mids of course...they just aren't the same.
The Harbeth and classic Spendors have at least something in common - that rich midband and classic box tuning which seems to give vocals in particular an organic presence, weight and roundness.
I owned the Harbeth SuperHL5 plus, and still own a little pair of Spendor S3/5s and even those share that similar trait. I've been eager to hear the newer Spendor classic speakers but they are rare as hens teeth for audition.