Mod my Rega P5 OR...time to move on ??

Adding mass is where you are likely to see the most improvement but unfortunately cannot realistically be "upgraded". 

Regards

Former P5 owner and long time record freak here. 

If you're simply into  hearing your records at reasonable/affordable level you're  fine.
Upping your game in step with the rest of your system will make you aware what the P5 lacks, and would never have regardless of tweaking. 

IMO, you're  standing at the crossroads of the audio abyss.

The P5 will not, even with the PSU, spin the platter precisely with a record@33.3 unless it has an AC motor regulated with a  Phoenix-type controller. Putting a $1K+ LOMC on  a P5 is questionable.You're already at the point you lost a  minimum HALF of your investment.

I sold my tweaked P5 at massive loss, but the new owner  was thrilled!
Its a buyers market used. Plenty of choices and you're in the drivers seat.

My ears are pleased,but my wallet isn't.There is no right answer. 

tablejockey: "IMO, you're  standing at the crossroads of the audio abyss"...Yep, been on this path for sometime now, I just haven`t changed components at a pace some do. Just looking to move up like most of us.

Used for sure....What did you go to from your P5 ?

I chose VPI, and have no regret. I equate the Classic as the Rega P5 within the line,regarding value. Currently, it may be the Prime. I see them listed at great prices, and it's a step up from the Classic. Mine is 5 years old and going strong.
The only mistake I made was purchasing new.

With that in mind, a used Classic can be found cheap, or better yet an Aries?

If I were starting fresh right now, I would go Prime. Be prepared for a pleasant surprise whatever you decide. That will be a game changer, like going with a tubed phono.. The 3D arm on the Prime, along with your Herron should put that ZYX in its best light.

Used in the 3-5K(especially the upper end) will remind you what the fuss is all about. 

It really depends on which way you want to go? Heavy Mass loaded tables or stick with a rigid light weight design like a Rega RP8. If you like the Rega sound and are looking to improve upon that in terms of detail, refinement, clarity, finesse, power and a table you can upgrade and tweak to your hearts content, look at a J.A. Michell Gyro SE. Its not rigid or mass loaded  so its not super heavy or light (tension spring suspension).  This will be the last table you buy, I promise. 

Matt M