I once tried to upgrade a Rega 3. In the end I eventually realised it was a little presumptuous to think I might know the Rega 3 better than Rega did. Even the so-called isolation tweaks didn't achieve the expected results.
Rega decks seem to be balance of very carefully matched resonances. Not so easy for the layman to improve at home.
My Rega 3 seemed impervious to any of my attempts to improve it.
In the end I bought an LP12, but that's another story.
In fact if you say that all turntables are a basically a combination of resonance control and speed accuracy, then it's not altogether obvious how any of these tweaks might have worked.
Oh well, no worries. It's all a learning process and many of us have been there before you.
A 1990 Rega 3 is not the last word in scale, bandwidth, or temporal accuracy, so good luck with getting a far better deck in the future.