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

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. 

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. 

http://www.usaudiomart.com/details/649386311-vpi-prime-6-months-old-2800/

http://www.usaudiomart.com/details/649383010-new-in-box-vpi-classic-1-turntable-with-jmwclassic-1-to...

scm-2 listings that can still be negotiated for less.
The Classic is about double the cost of more mods, and itsa NEW table, clearly superior in build. Since sonics are subjective, just how much "better" it is than the P5?

For a little more, the Prime will have the nicer arm and VTAon the fly.

I will say the modded P5 is reasonably close to the Calssic,but the stock Classic is closer to an uber table more,then any modded P5 will ever be.

Youre treading dangerous waters $$$ dumping more money into that P5

I'm curious to see what the OP decides on, since my path was similar.

I certainly miss the simplicity of the Rega philosophy-just put a record on and lower the arm.

The difficult decision however, is where do you draw the line on tweaking$ and justifying the sonic improvement? 

Post made while listening to my now dated stock Classic(except Mapleshade brass footers and obscenely price maple slab) with Audio Technica ART9.

My P5 just couldnt keep up with the VPI. This of course is my subjective opinion.

slaw, the wall bracket you have there in your profile looks interesting. I hope your project was a success?

Im fortunate the 100 year old wood planked floor of my place doesn't add the footfall dilemma. I find the low tech(and pricey) Mapleshade philosophy doing its thing with my table.

At this point, only a MAJOR$ system overhaul would satisfy my ears, and that just ain't gonna happen because I'm about $75k short!