Why Upgrade the Rega Counterweight?

I have an Nad 533 with an RB250 arm. I was very skeptical that changeing the counterweight could make any difference.
Boy was I surprised when I installed a Michell Tecno Weight. The bass was tighter and had more slam. The overall tracking seemed to improve and everything sounded better across the board. It was not a subtle improvement.
Highly recommended. I also installed the white belt but the old belt was so old and stretched that I can't comment on the sonic differences.

I have heard many good things about changing the subplatter
also.

You would also need it to use a heavier cartridge, like the Denon 103 for example.

I changed to the Origin Live endstub/counterweight. Seemed to clarify everything. That said, I would not recommend investing in incremental upgrades to Rega arms. It is money down the drain, at resale time. Better to save up and get a better arm.

The white belt: I bought one and cannot really say it maakes any difference. The white belt was supposed to be a 'limited time offer' so I decided to try one.
I plan on a subplatter someday on my Rega P5. and maybe the type of counterweight that hangs below the arm and rides on two fine 'rails'...
I can say I asked for a different stock subplatter, as when I bought the TT last Spring, I asked to see it in action, annd could see a tiny variation in the glass platter movement, and they let me swap the subplatter with the demo unit. (which was perfectly flat) the movement up and down was only about the thickness of two sheets of paper, but hey, I want it right.
So the stock plastic subplatter can have flaws...