Generally, it's best to follow the directions of the speaker mfg with regard to whether use spikes or other footers based on type of floor. You especially don't want to mess with speakers that already account for a certain resonance with their cabinet. Many speakers use this to their advantage versus trying (usually in vain) to rid all cabinet resonances and floor born resonances.
On the flip side...a lot of speaker makers don't put much effort into their feet/stands. In those cases, I would actually recommend this one combo that I've found works generally well. Take the spike footers that come with most speakers/stands and insert them into Oyaide INS-BS pucks. Whether it's on wood floors or carpet, they seem to have a positive impact for a much more reasonable price than other exotic options.
Another option is to construct a sandbox with a floating top and put your speakers on top of that without spikes. Nothing dissipates the significant vibrations of speakers while also providing a solid base like sand...especially at a cost effective price.
