Isolation works to reduce parasitic sympathetic vibrations from floor and walls. For TT and tubes this also helps reduce feedback from floor/wall vibration. Other electronics are not sensitive enough microphonically and do not benefit except some equipment might last longer in an environment with less vibration...
No brainer.
Thin wall speakers can sound good but the thin walls add coloration and often change the timbre of the mid range. In principal this is bad design, however, some really like the sound. Thin wall cheap cabinets are lighter and allow for reduced shipping packaging and lower shipping costs which is of huge benefit to the manufacturer/retailer - and if with some hand waving marketing hype the listeners can be convinced that light weight is technically beneficial (just like a TT) then you can easily understand why there are thin walled light weight designs...
