is turntable isolation required?

I have read opinions saying that solid plinth turntables absolutely require some kind of isolation platform to sound their best. Would you say this is correct?

my Thorens TD-850 weighs 21 kg, very solid plinth, sits on spiked feet that have a small, built-in layer of what appears to be viscoelastic material (presumably providing a very small amount of isolation), on a Billy Bags stand. Solid floor. I had it on a Bright Star (sandbox-type) platform, but couldn't really hear much difference, if any, with or without it.

If I'm likely to hear a real benefit an HRS S-1 platform looks appealing. Other recommendations welcome.

that it be cost-effective might be too much to ask, in this hobby.