Passive or not, every component is near equally susceptible to capturing air-borne vibrations which are typically far more prevelant than floor-borne vibrations. However, if a component has a motor and/or power supply, that is simply additional vibrations and resonance generated from within (rather than without). Regardless of the source of the vibrations, they still need an exit path away from the component.
I'm aware of only one mfg'er who considers MDF the material of choise for any serious type of vibration control and I know of no mfg'er who considers aluminum the material of choice for a cone, spike, or point.
If your budget is tight, perhaps the best little DYI project might be to pick up a smaller 1" thick hard maple cutting board, perchase three appropriately sized Audio Points from StarSound.biz that are tapped for perhaps 3/8"-16 or 1/4" thread and then purchase the appropriate carriage bolts or set screws to secure the Audio Points to the bottom from above.
You're probably looking at about $60 or so in materials and I doubt that you'd find any better performance at this price.
But this methodology is not isolation. This is mechanical transfer.
To the best of my knowledge, there is no such thing as total isolation from unwanted air-borne vibrations. Often times you can dampen by placing your component in a sandbox but the sonic effects should be a bit more unpredictable.
-IMO
