If you use solid mounts you will lose all the vibration insulating factor that the mounts were designed for. If you use polygraphite you will get all of the advantages of the solid mounts and retain some on the insulating factor the mounts were meant to give.
Subframe connectors are designed to give your subframe a stabilizing factor. The rear wheels can push directly on the frame when connected, instead of the sheet metal floor being part of the 'push'. The polygraphite mounts will not take away any of the 'push' factor. They will retain some of the insulating purpose even if you have connectors. All cars have insulating mounts for ride comfort. I would really think about it before I eliminated them, that's what you do with a solid mount, you are eliminating the mounts your 1st gen was designed to have....