Our cars WERE built with rubber bushings. The reason that people are replacing the bushings is due to their being over 30 years old, and in doing so, are looking at some alternatives, like metal or polyurethane mounts. One of the reasons that our cars ride as well as they do is due to the transverse torsion bar front end. Ma Mopar managed to get a ride almost as good as the big C bodies in a smaller car. However, part of that is the use of a lot of rubber (including the K member mounts) and a sub optimal geometry for high G force turns. However, some people want the cushy ride, some would prefer a tighter, more precise front end feel. People who look for the tightest front end go with solid metal (steel or aluminum). People that want a soft ride get original rubber replacement mounts. Some try to retain most of the soft ride while getting a firmer front end use polyurethane. All have proven track records as being able to stand up to regular street use. Delrin may be able to do that, or it may not. I don't know, but where it fits in the firmness/rigidity spectrum between metal and rubber mounts is an open question as well. The weight point is not an issue in the vast majority of cases for our cars. Even if the Delrin mounts weighed nothing, the total weight reduction is probably no more than 30 lbs,, probably less than 20 lbs. vs. polyurethane or rubber. In essence, it doesn't matter, considering that weight of our cars. In a road race car, where effort is made to get to the absolutely lowest weight (within the regulations), it is far more important.