I've never driven in a car with solid subframe bushings, I have the poly ones in my front, and they are fine.

I imagine solid in the front, you would feel every little vibration from the motor. Front control arms will still have rubber bushings to isolate turning/suspension vibrations from the rest of the car.

The oem sleeves are a VERY tight fit into the bushing, He said he almost maxed out his 30ton press getting them in. I said I need guys to be able to install these with a 12 ton home garage press, so he said he will loosen up the tolerances for any future batches. I'm sure there wont be much room for contaminants to get inbetween.
The bushing to subframe would be a good idea to lube up, just like the replacement poly ones, as they are not injected and formed to the sleeve inside the subframe.

I plan on powdercoating everything obviously, before install so I am hoping it seals out the majority of crap.