Spikes don’t isolate, they couple. Unfortunately the Hifi world is full of bullshit like this (see also Cable Risers, exotic power cables etc.). This advice is not Hifi voodoo but physics/acoustics based (I work in music studios):
The main improvement you can get is by getting the speakers in the right position (height and width). I’d invest in some decent stands that put the tweeter at ear height. Try to arrange the speakers and listener in an equilateral triangle converging about a foot behind your head (ears are on the side you see). Distance to walls will change the sound – contrary to popular opinion, in small rooms it is often best to put the speakers very close to the front wall.
Sorbothane spheres are probably the best option for isolation and are relatively cheap. Make sure you get the right size for the weight of your speakers. This is just icing on the cake though really – speaker cabinets don’t really move that much in use. If you really want to improve the sound think about investing in some acoustic treatment.
This guide has some solid advice on speaker setup if you want to know more (studio focussed, but the physics is the same):
https://www.genelec.com/sites/default/files/media/Studio%20monitors/Catalogues/monitor_setup_guide_2017.pdf