Will a phono pre-amp make a substantial difference

@mylogic

AI which can say anything, and is ultimately accountable to no one

Your logic is probably based on the same sort of neural network that large-language AI models are based on, but is probably less able to succinctly summarise in neutral ways. 

I personally find it astounding how helpful AI can be in many different situations.  Ai will not say anything that has not been said before, and the fortunes of the technocrats currently investing billions depend on how we humans accept what their competing AI models produce.  The authors of these models are accountable to their bosses and the shareholders that back them.  AI is currently the biggest enterprise in play.

To assist the OP, I am a Phonostage Enthusiast as the minimum. 

Posts shared on this forum, makes it known I have carried out extensive travelling and footwork to experience a wide range of Phon's. 

SS, Valve Hybrid, Valve Input /Output, produced as Commercial Design or DIY Design /Builds are heard by myself in large numbers.

The result being I own  all types of Phon' listed. 

I can also take a TT from storage, which I occasionally do, and put little thought into the TT's basic requirements. 

When heard through a owned Phon', the TT's shortcomings are immediately recognised. 

A little effort put towards the TT's needs changes the impression immediately. 

This requires little thought towards the electrical support for the TT, to perceive betterment is created. 

The electrical support through producing End Sound clearly shows the benefits of the changes made to look after the TT's basic function. 

IMO the phonostage is very important and can make a huge difference. The Rega MM MK is a great choice and will pair well for you. I had one with MY P3 for several years until i upgraded to an all tube Zesto Andros Audio Spirit. 

You will be very happy. 

Sutherland KC Vibe and also, get a Groovetracer subplatter for your P3. One of the most significant upgrades you do.

Since you have a NAD M33 with digital inputs you might want to consider a phono preamp that converts to digital a lot sooner in the chain.   Check out the recent review for the miniDSP ADept on Audio Science Review.
Product details available here.