Would an Isolation TT platform further improve my TT?

Adding more mass to your setup is unlikely to address the one remaining source of vibration that you are not currently tackling -- subsonic or seismic vibrations that are being passed to the table from earth and result from traffic, construction or seismic activity.

Solutions such as a Minus-K platform or a Herzan like active isolation system would be worth exploring, but are both very costly. The poor man's alternative is suitably tuned springs, perhaps a set of such under one of the platforms you are looking at would be appropriate

I have always found that the more rigid the support, the tighter, more incisive and clearer the sound. Damping of the support by using wood or "absorbers" softens the sound. Marble and glass sounds etched while oak sounds warm etc. I'm old school and have to be convinced otherwise but spikes, cones and inertia allow the table to be as fixed as possible. There is also a school of thought where springs in cups provide both isolation and rigidity at the frequencies that matter so look into that philosophy also.

Symposium acoustics sells their Segue ISO platform for just this reason, they use their sandwich technology and add a set of 5 special springs to the bottom, I use one on my 70lb Prime on top of a 3" slab of butcher block on top of a lead balloon turntable stand and in another system it really earns praise supporting my Origin Live setup in a much more needed application. These are less than a $1000.00 and available for different weight loads. Enjoy the music.

I will look into the Segue ISO. Looks interesting. My TT is 55 lbs. so the medium platform would cost $549.

Symposium discovers springs. Whoa! Shut my mouth and call me corn pone!