The uninstaller isn't working correctly so your system is slowed down constantly by a bloated driver that only a few games use.
Sorry, that's just not true. These "drivers" are simply DLLs used by game applications, as far as I know there are no background processes running, so they do not slow your computer down. There might be drivers active when using an Ageia PhysX card, but I'm sure any overhead is minimal.
Before wasting my time coding for it, i'd rather go down the multicore / multigpu road.
Most people don't know that the Ageia PhysX SDK not only supports their own hardware acceleration, but it can take advantage of multi-core processors. Yes, this means that even an unthreaded language like Blitz3D can take advantage of multicore processors if you could wrap PhysX for Blitz3D.
There's really no reason not to choose Ageia PhysX SDK unless you don't want the 30MB "drivers" or if you want cross-platform. So using Ageia PhysX SDK means your game is automatically compatible with: Single core users, Multi core users, and PhysX card users.
Do people really care to spend on hardware just to see slightly increased numbers of particles/small objects being bounced around the scenery? This is what PhysX cards seem to have been doing up until now.
PhysX cards simply accelerate the physics capability of a computer. Nobody minds extra processing power, it's just that hardware dedicated to physics only seems kind of wasteful.