I originally installed my Gaias with the carpet cups/spikes - the cups/spikes are a real pain to get set correctly. That said it was worth it for the improvements that others have outlined above.
Eventually, I tried the Gaias without the carpet cups/spikes and there was no loss of the distinct benefits that the Gaias brought to the show. My view is now that the carpet cups/spikes are completely unecessary.
This was carpet over a suspended wooden floor. Others may have different experiences.