Firstly the impact a Rack can have, is not limited to High Quality Devices only that will benefit from a well thought out Rack.
All devices mounted on a Rack that interfaces as a betterment into the Listening Environment will clearly show benefits are to be attained for the produced sonic.
Listening Environments are quite unique and 'all', will have a variation of the ambient energies able to be transferred into the Audio System.
One design for a Rack, that works within one environment does not guarantee the same Rack will produce the same results in another.
The situation could be a Rack of a certain Type might need additional support Structures used in conjunction with it to get the best interface from it.
Alternatively a completely different Rack Design might be the only method to achieve the optimised interface in a particular environment.
Note: There is not a ubiquitous Support Method that extends to creating a optimised interface in all listening environments.
Something that is overlooked and not seen too often as a Topic of Discussion is Cable Management.
Carefully routed Cables and Cable Tidiness, are able to impact on the sonic produced.
This is ubiquitous across all listening environments, if the Cables are a mess, there will be a loss to the quality of sonic produced in the listening environment.
When a optimised Support Structure is discovered, and used for supporting a audio system, that has thought put into producing a Tidy arrangement for the Cables, the most basic of benefits will be a noticeable improvement in the Bass Note and the Decay.
Additional Benefits will be a coherence through out the frequencies, where the Mid's and Upper Frequencies are perceived as having a projection.
Ultimate Benefits that can be perceived are Micro and Macro Details will be noticeably present, and even better, the Envelope of the Notes/Vocal will manifest with a shaping to the point they can almost seem tangible.
It really does come down to how much an individual is willing to experiment with Structure and Cable Tidying to get such perceptions on improved sonics.