Super pro and a few others have a lifetime warranty so if they degrade like above they are replaced by the company. No labor paid for though.
Rubber was used by the factory for a compromise between compliance over bumps etc and performance.
In a performance application, rubber allows more flex or geometry change and less precise handling. whereas nolothane et al maintain geometry better but increase NVH. Rubber can last along time but the absorption of chemicals like fuel and oil degrade their stiffness. they look good but are like jelly. I haven't seen this happen with poly bushes.
I have poly in all bushes in all of my cars and haven't ever had a problem with crumbling. In the race car and hipo road car I have had to replace certain poly bushes (same location in car) many times but would have done so with rubber as the loads placed were much greater than the factory had designed for. the 2 part poly was always easier than 1 piece type original rubber especially those with steel casings
Just my thoughts
JP