Max Townshend has a 25 minute video on You Tube discussing the topic of vibration and it's effect on hi-fi (he has done a lot of research on the subject, and is considered an authority in the field). In it he covers spikes, and states as fact that they are just as efficient at transmitting vibration up them as down. The video is definitely worth 25 minutes of your life.
Max makes a great isolation product, the Seismic Pod. Unfortunately, it costs about $200 for one, and you need a minimum of three for any item placed on them. A set of six (three per speaker) will cost you almost as much as the LS-50's, eight more than the speakers!