At the resonant frequency of the floor, decoupling isn't going to mean much. At other frequencies, the mass and associated inertia of the floor will dominate things. You'd need some pretty powerful speakers to overcome that.
IMO, pointed spikes and cones are good for chewing up your flooring or subfloor, and not much else.
Meniscus Audio sells some nice brass cones with a rounded tip, and they're not very expensive. They work well on carpet. I think they should be ok for oak flooring too, although I don't see that you need cones or spikes for hard surface floors.
What is the resonant frequency of the floor?
Wouldn't it be dependent on a number of variables?
So, the only frequency that could be induced by a speaker's vibrations is the floor's resonant frequency?
Couldn't a wood floor amplify vibrations tranmitted to it from the speaker?
If a speaker is sitting with rounded spikes on a wood floor, should there be any concerns that spikes are acting as conductors of vibrations?
Why use any spikes at all when placing speakers on a wood floor?
Wouldn't it be better to have as much surface area as possible in contact with the floor?
I believe it makes more sense to use a dense, not absorptive pad between a speaker and a wood floor.