I have found that vibration control is a critical part of maximizing the performance of the system. However, I think "YMMV" applies here more than in any other area. The factors that will affect the performance of footers include: the composition and stability of your rack, the component chassis, the overall resolution of your system, the type of component (tube/ss), the microphony of the tubes, the type of floor in your listening room, the energy thrown into the room by your speakers, etc.
There are reputable companies like Stillpoints, Nordost, and Symposium who make excellent products that clearly reduce vibrations and change the sound of your system. Whether it's for the better only your ears can tell you.
Best, Scott