In short, No.
Physx is bearly noticible on nvidia cards right now (physx needs about 64mb of ram for crazy good capabilities, and nowdays GPUs have about 1 GB+ of ram, so it wont impact your GPU performance).
It was a great idea back when CPU had to deal with physx and nvidia didnt have the technology, now, not so much.
Also notice that Physx is implemented by game developers, so they are unlikely going to add so much of it that only a customer with a dedicated Physx card can enjoy the game at its maximum quality.
If you are looking for a powerfull upgrade for your PC, id recomend checking Audio upgrades (good speakers for example), as apart from video , audio is the ther way the PC delivers pleasure to us gamers .