How important is low W & F performance anyway?

Answer, if you cannot hear it, it does NOT matter, and published specs, ridiculously low, are a marketing game.

I've been given, inherited, and purchased a good bit of Vintage Equipment.

I think it is fair to say that old published specs compared to modern: Vintage Equipment has higher distortion, higher wow and flutter specs (real or marketing numbers).

And yet, when you listen, and end up preferring that Vintage equipment, you learn that the low decimal numbers do not translate to 'better'. 

My Fisher 80 az mono blocks, made in 1958, were rated at 30 watts per channel at 0.5% distortion, I have seen many Vintage manuals that showed power levels at 1.0% distortion as a threshold.

https://www.fisherconsoles.com/non%20console%20manuals/fisher%2080az%20sm%20om.pdf

When Steve Leung at VAS heard I was going to sell them, he made me sell them to him. I was just there to pick up a friend's cartridge he rebuilt, and Steve mentioned he had finally found time to listen to them, with a big smile.

My Thorens TD124 TT speed, you waited till it warmed up, refined the speed, and learned to check it once in a while, especially if a party and the room warmed up as more people arrived. Only very rarely could I hear the speed was off (young ears back then), most of the time I was surprised it had drifted and I couldn't hear it. No one at the gathering ever knew.

Technics TT's. I often recommend buying an SP-10, 15, 25, and I link this document to show that the specs of current models might meet, but do not exceed those vintage models shown on the bottom of the chart

https://vintagetechnics.audio/turntables.php

What is of concern is living without features, buying into 'straight wire with gain' that leads to no balance control, no stereo/mono mode switch, no rumble filter to help with slightly warped lps, no tape loop .....

Quickie AI:

"Wow and Flutter refers to speed variations in a turntable's rotation that cause audible pitch distortions in the music.  Wow is a slow fluctuation in speed, often once per revolution, typically caused by an imperfectly round platter, warped records, or off-center pressing.  Flutter is a faster variation, usually due to motor pulsing, bearing issues, or belt imperfections, and is perceived as a "warble" or "cracked" sound. 

• Audibility: Most listeners won’t notice wow and flutter below 0.25%, though sensitive ears may detect it at 0.10–0.20%.  Values above 0.25% are generally considered noticeable and problematic."

Audibility: Most listeners won’t notice wow and flutter below 0.25%, though sensitive ears may detect it at 0.10–0.20%.  Values above 0.25% are generally considered noticeable and problematic.

Therein lies my question:  How can a table such as DD1 have such lousy performance (0.8%) and still garner nothing but praise?

OP

"How can a table such as DD1 have such lousy performance (0.8%) and still garner nothing but praise?"

You had it, tested it, (lousy performance) but could you hear it?

I thought the bass was bloated, the opposite of tight like when you hear bass through the walls of an apartment (BOOM...BOOM...BOOM).  Other than that, I thought it sounded reasonable.  But I’m not a professional reviewer and my ears are not very good.

On DD1, the primary W&F response was the cogging at 88.88Hz which I'm not sure what that would sound like (vibrato?) and I certainly wasn't listening for it.  I actually didn't discover it until I increased the BW of the software to 100 Hz.  At 40Hz BW, it wasn't visible.

On DD2, the table came sans tone arm so listening wasn't possible.  The primary response would have been 13.33 Hz which should be within the most sensitive area for human hearing (wrt to flutter: 6-20Hz).

To an extent the answer to how important something like W&F specs are will be dependent on the sensitivity of the individual.  I use sustain notes on a piano for ear tests.  Using AnalogMagic my worst numbers according to my notes are for my old VPI HW19, and W&F is typically 0.10-0.13 which is not audible.  My SL1200GAE measures 0.06 and the HW40 is similar.  Most of the DD turntables that I have measured so far seem to be in the 0.06-7-8 range.  Elliott nailed it, if you can't hear it, it is not important.