For those who balk at the price of the Townshend Platforms: imo the individual Seismic Pods can work just as well, and are considerably lower in price. If your loudspeakers have outrigger bases, the Pods (or the IsoAcoustics GAIA) can be installed in place of the stock spikes.
No outriggers, and you want a larger footprint base for your speakers? Get a 3/4"/19mm piece of Baltic Birch ply, cut two identical pieces, put a piece of ASC Wall Damp between them, screw together, paint, attach the feet of your choice, and install. Best upgrade for the money!