Tone, Tone, Tone !

Beauty is on ears of beholder. 

The Rega RS1 speakers on my desk give me tone, clarity, and speed so I totally understand your relationship with your Spendors. 

I have tried to replace them so many times with other hyped speakers, but each time I end up not keeping the replacements. 

The RS1s do lose their magic in a larger room. 

To answer the OP question, "non-fatiguing" was a huge priority for me. Read on.

But first, to respond to the inner thread on Harbeths-

So what I see is a bunch of speaker design "no-nos" all of which coincidentally reduce the
production cost that are then presented as a viable design methodology that doesnt make sense to me and also runs counter to the design philosophies from speakers that I think sound best.

Well, I completely disagree about "homogenizing", but YMMV.   I think it's a stretch to say the whole line of speakers is representative of "inaccurate" designs when most of the recent model line at least measures more accurately than most speakers.

The "no-nos" were one of the things that intrigued me in the first place.  It's counterintuitive that optimizing an older, resonance-managed, design is not only appealing to a ton of experienced listeners but also *measures* flat.  And Harbeths just refuse to sound the way their looks prejudice me.  But it's worth noting that Shaw prolifically defends and explains his methods and design choices on the forum.  And he's made significant and expensive changes to the original design in terms of driver materials and crossover design, so they haven't been sitting still.  I hadn't heard Harbeths before recently, but clearly many people think the last few years have brought huge improvements, particularly with the proprietary driver/material.

As for phase coherence, I moved over from Thiels, much like @prof ,  Thiels famously optimize around phase/time coherence.  Honestly, the Harbeths were the only speaker I heard in my last round of auditioning that (and forgive the imprecise analogy) offered as clean a "window" onto the sound as my old Thiels, while providing an even more lively and natural-sounding presentation of instruments I know well from live performance.  That's where I get the "tone is just right" feeling others are referring to here.  Their marketing catch-phrase is well chosen.

I listen to music for hours every day*, and there can be no doubt that a major search criterion for me is "non-fatiguing".  I was happy with my Thiel CS3.6 for 25 years (!), and I'm becoming similarly wedded to the new SHL5+ (Anniv).

Now, Harbeth's ridiculous additive model naming, that's seriously fatiguing.  I suppose some model down the road will be the "Super HL5 Plus Ultra Enhanced Anniversary of Anniversary Edition"

*as I write this, I'm listening to the Sony Classical/Sol Gabetta-Schumann recording on Tidal - lovely open-sounding recording, close-up image, and lovely tone in my living room.

Prof, The reason ESLs sound "skeletal" to you, and I hate sounding like a stuck record is that the ones you have been listening to switch radiation characteristics in the mid bass. They are acting like linear arrays above 250 Hz but like point source radiators below, square of the distance versus cube of the distance. A linear array has to be taller than the lowest wavelength you need to reproduce. Their ability to radiate power drops off dramatically below 250 Hz as you move away from the speaker. Add dipole effects to this and you wind up with wimpy bass. This is what glued everyone to the Acoustat 2+2s. They were the first planar loudspeaker that did not do this. The Soundlabs you want to listen too if you get the opportunity are the Majestic 845s in an 8 foot room or the 945s in a 9 foot room. A linear array that terminates at boundaries above and below acts as a linear array into infinity. At the beginning of Roger Water's Amused to Death is a segment with a barking dog. A friend's medium poodle went ballistic when the dog started barking. Never play Amused to Death with someone's dog in the house.
This notion that dipole subwoofers fit dipole speakers better is faulty. There is just no getting away from the cancelation and front wall effects. The result is very lumpy frequency response and no bass at all below 40 Hz. They will make the satellites sound better as long as you are crossing out of them but that is about it. The mistake people make is trying to match a point source subwoofer to a linear array loudspeaker. Linear array subwoofers either have to be as tall as the room or as wide as the room. That is a lot of woofers.