I have a very modded (some may say fully modded) P5, and it is still better than the Simplex, but I would say I enjoy both very much. The P5 has a touch more air, is more resolving, and has better extension. The Simplex wins out in low noise and ease of setup and maintenance.
I had the VPI Classic for about a month to compare directly against the P5, and the P5 won handily in all around musicality. The VPI could pull out more info, but at a steep price in lowered musicality with 85% of my LP collection. Definitely NOT a good use of money to my ears.
I have the full set of GT mods (subplatter, Delrin platter, and Counterweight), rewired the arm with Incognito copper, added VTA adjustment with Riggle's VTAF, fully decoupled the motor, added the double belt pulley. These are mods I paid for, mostly used.
I then "copied" the Rega RP3/6 series design by adding a DIY carbon fiber brace between the plinth and arm, and that really brought resolution and resonance control up a notch. Without the brace, the P5 is a bit less distinct, fast, and resolving, but always musical and enjoyable. I've also added DIY damping to minimize distortion (Delrin bearing collar, Herbie's grungebuster). See the Rega thread at VinylEngine for the full details.
Then I added an Audiomods Classic arm, and boy what a difference that made. No longer use the GT counterweight or VTAF, but they are good upgrades nonetheless. They just won't work with the AM arm.
The bottom line is: the P5 is a great machine to use either stock or in upgraded form. Sure, you could spend $2.5K on a Simplex or VPI, but spending the same amount you could be just as happy with a used P5 with mods and adding an Audiomods arm. If you are handy and your system is revealing enough, you will be paid back with every mod/upgrade/tweak that I've done.
That said, if you want simple and satisfying, the Simplex will also take you there.