I want more from my Rega P5

Regas are extremely sensitive to being absolutely level. When slightly out of level the sound can be harsh. I guess this is due to rocking in the main bearing. So make sure it's absolutely level.

Also, since you bought it has it ever been stored in a manner that might allow any oil to leak from the bearing ? Regas also are very sensitive to having adequate oil in the bearing, of a sufficient viscosity.

I think the power supply may be a good upgrade as speed stability is critical in LP replay, but unfortunately speed stability is not the strongest element of the Rega.

I can't recall whether or not the P5 uses a Rega RB300 tonearm. If it does an upgrade to a Michell TecnoArm (a heavily modified RB250) would be in order. I firmly believe that it is a world-class tonearm at a budget price, and is capable of getting the best out of much more expensive cartridges than have been mentioned here.

Just adding a modified weight or getting a rewire is not enough. The Michell mods are the whole deal.

some upgrades fo me on an NAD533 which is a cloned P2 have been:

Michel Technoweight (end stub and counterweight)
replaced feet with isopod feet/cones
TWL Strange Tonearm Tweak (search this forum for that one)
DeepGroove subplatter
Teflon arm wrap
DIY spotmat

Each change brought about noticeable improvements and together the sound has brought about better definition overall and on attack/decay, detail, dynamics, 'swing' aka PRaT.

Have a look at this: Rega Review

The P5 uses the RB700, an evolution of the RB600 on the P25.

Twochannel guy, I can only offer from my experience. I upgraded my P5/RB700 to Incognito wiring. I found nice improvement there. Later, I upgraded to the TT-PSU. In my opinion, this is a mandatory upgrade...it elevated the table's performance significantly. It's a nice table with the TT-PSU, wall shelf, and proper setup. If you can't do a wall shelf, buy an Ikea Lack table top and screw some cones into it and set this on your rack with the Rega on top. I used this before the wall shelf and it also worked. The P5 is a nice table. Enjoy!