Would an Isolation TT platform further improve my TT?

For an iso stand stiffness is highly desirable for the top plate since a stiff top plate better resists bending forces, I.e., rotational seismic forces. This is why 3” maple boards sound better - generally speaking - than 1” maple boards. They’re stiffer. It’s also why some of the big commercial iso platforms use thick granite slabs for the top plate. It’s also why I use thick granite or bluestone slabs for my stands sometimes.

You guys sometime make me want to pull out whatever hair I have left. You are spending someone else money without analyzing the situation.
The TT is sitting on a heavy stand on a concrete floor. There is no isolation platform that is better than four inches of concrete and there is no isolation platform that will help in case of an earthquake! If you are more worried about isolation then get a SOTA or an SME or a Basis. Those turntables do not care what you put them on. 
Luxmanc138 spend your money on another cartridge or more music or taking the wife out. Buy her some flowers. Your turntable is just fine where it is. Don't fix problems that do not exist.

I already explained that the building and everything in it - including the cement slab - are vibrating right along with the Earth crust motion, at frequencies between 0 Hz and 20 Hz and higher. The peak frequency of Earth crust motion is around 1-3 Hz. Now, I’ll grant you, that cement slabs are not very affected by rotational forces.

And, the seismic vibrations traveling across the Earth's crust are, Max Townshend claims, many times greater in microns than is the distance a tweeter travels when reproducing a not-that-high a frequency. As are the vibrations that swamp the squiggles in the LP groove the cartridge is attempting to measure.

Not to be too picky ⛏ but it’s actually that the Earth’s crust is moving like a wave, that’s what produces the *very low frequency* up and down movement of the building, and the horizontal movement of the building and the rotational forces that try to rotate and twist the building. It’s just like someone shaking out a carpet. This is not to say other things produce seismic type vibration, you know, wind, wave action, traffic, subways, footfall, fans, etc.