I have been thinking about using the solid mounts too. But I'm not sure if it really is much better than the poly mounts. Mike Rainbird also used the poly mounts on his track Escort and never noticed a bad thing about them. Though I agree that for the handling it can only be an improvement.
One thing I would be a bit worried about is that the bolt might work loose from vibrations. With the poly bush you compress the bush, putting some pressure on the bolt that will prevent it from coming loose. But with a solid mount the bolt only needs a little movement to release the tension.