Can an audio rack be that important?

I couldn’t have said it better than @mikelavigne 

Just to add from personal experience - I have found my system to sound best with the amp(s) on the floor or on amp stands, away from source components. I have proven this to myself with every amplifier I owned once my system reached the resolution levels to reveal subtle differences like that. 

I think that it is likely that without exception, all those who have posted that good quality racks make no difference have never experienced the difference that a good rack makes in sound quality.

Like a real genuine Omega Speedmaster vs a fake from China. 🙄

To the OP’s question, I find his subjective quality characterizations interesting:

• a good audio rack
• ultra high end audio equipment
• sub-par equipment racks
• a high end audio rack
• a reference rack
• high quality components

These types of subjective quality modifiers have been used widely throughout these forums, and throughout this thread, and I often wonder what level of correlation exists between the meaning of these phrases when used by various authors.

In this case of audio racks, I am interested in what physical/mechanical characteristics take an audio rack from the realm of being sub-par or basic to being good, high-quality, or reference? Racks costing thousands of dollars are made by a variety of manufacturers, from a variety of materials, using a variety of assembly and support methods. What makes an audio equipment rack good?

What makes an audio equipment rack good? Making it as non-resonant as possible is a good start, which often involves some decoupling of the shelves from the rack superstructure. Racks do make a difference to sound quality but they are best considered in the same context as the general category of resonance management devices.

Of course they have to be suitable for the equipment being housed and aesthetics matters a lot to some people.