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.
Some, yeah.
I have suspended wood floors. i use a wide, sand filled struts, TV type rack from a bigboxstore.
My TTs are on the top glass, with 5" round 3" tall cement patio blocks under them. The Rega P5 is on a VPI isolation sprung device i got for free, on top of the bricks. The Kuzma is on a hardwood board, which is on rubber stoppers on top of bricks
So my isolation is totally 'duct tape' level junk, but it works fine for me.
Some is good. a lot is for folks who worry a lot.
I think it all depends on your turntable.... Linn tables love to be on a very light table since the resonance of that light table will be disipated by the suspension of the turntable. VPI's on the other hand love to have a heavy, solid table to rest on. I had a Thorens at one time, but don't remember what I used. I suggest you try different things and see what happens.Your Thorens has a spring suspension ...from what I read, you have a very solid footing for the table except for those viscoelastic barriers. Try removing them which would give you great solidity, and see if that is any improvement.
Hi Lloydc, yes and no and depends on your table

If I was you I would do some searches and try and find some others with the same or similar table and see what they have done.

I have my table set-up where the floor moves a bit, I tried HRS "still own" and a few others but in the end got a Minus K platform and have never looked back. Depending on the size of your table you might be able to utilize their standard size offerings, unfortuantely mine was a custom size.
Unless you have shielded it from acoustic energy that is created as you play, it is not fully isolated, not matter the 'bricks and brac'. Moving it to another isolated room is generally the best way.
If your needle jumps when u walk across the floor or you hear acoustic feedback then u need some type of isolation. If not then your present set up is all u need. Sometimes people tend to go to extremes and this is overkill and expensive at that. I had a micro seiki BL-51 that had huge rubber feet that isolated it well. I also have AR turntables that will mistrack if I walk across the floor but the AR like the Linn always sound better to me. I must like the sound of spring suspended tables better but they are harder to isolate from footfalls. So I step lightly while the turntables are playing.
I love the Gingko isolation platforms with a slab floor. It stop much of the bass rumble. Until my most recent turntable, I thought it made a huge difference with my other turntables.