This has always been my opinion on the subject of speaker spikes:

Yes on carpet to help stabilize the stands.

No on wood floors - Use the disks that are usually provided.

Yes on subwoofers for clearance issues but only when used in conjunction with an Auralex GRAMMA (aka Subdude). The GRAMMA helps to isolate the sub from the floor. It can be very helpful in eliminating unwanted rumble and muddy bass.