The Speed Box offers a feature set that would lower the noise floor, improve resolution, and increase dynamic range: The Speed Box sends the AC input through a regulated and shielded component isolated from the turntable chassis. The AC power supply is off-chassis as well. Add in quartz-regulated speed control and that's a lot of functionality for $129.
Of course the soundstage would be deeper and more delineated, and the bass deeper. Those are the kinds of improvements you get when you keep AC artifacts out of the signal chain and thereby lower the noise floor. It's especially critical on turntables, where the cartridge's job is to amplify vibration. Keep the vibrations you don't want off the main chassis. That's what the Speed Box does.
Of course the soundstage would be deeper and more delineated, and the bass deeper. Those are the kinds of improvements you get when you keep AC artifacts out of the signal chain and thereby lower the noise floor. It's especially critical on turntables, where the cartridge's job is to amplify vibration. Keep the vibrations you don't want off the main chassis. That's what the Speed Box does.