Is Spiking Necesarry?

Almost forgot, IsoAcoustics just started selling isolation feet for speakers, in addition to their usual bases. Worth checking out.

Best,

E

mine sound noticeably better when I push the spikes through the carpet to make contact with my basement's concrete floor.  i do this with the subwoofer too.  
pain to move around but the sound is better.

on the other hand i was in the vinnie rossie room at AXPONA and he demoed his system with the harbeth's resting on top of the end tables.  
still sounded very good but a little loose / boomy in the bass if you weren't dead center.  

short answer- yes IMHO

Only if your guests are having trouble loosening up.

Years ago, I brought home 3" thick granite surface plates. I placed my speakers directly on them without spikes.  Floor was concrete slab. Sounded great so I would not say that spikes are always needed.

movement of the entire box back & forth will modulate the cone movement - causing phase error and other horrible things

so you want a way to prevent that - spike or very heavy cabinets will work

or... buy electrostatics or Maggies - problem solved (and a lot of other problems are solved too)