Back in the thread a fair way I mentioned I’d 3D printed a pair of these and thought there was a general improvement in the feel of the car after fitting and left them on. After that, a few of weeks ago I had the Eibach -30mm coils fitted (and full geo setup) and have got used to the more direct feel of the car.
When I first fitted the printed door bushes I was aware they were not tight in the cups; not loose, but they slid in without sanding so I made a pair .3mm wider and could feel these were a quite solid fit to the sides of the cups. I did a (roof up) run over roads I know well including our far from perfect approaches to the village and the result was the ride felt the same but there was a lot of squeaking and rattling from the roof I didn’t have before; quite unpleasant.
I then gave my original rubber bushings a good squeeze in a vice as suggested by Saz9961 somewhere up the thread. There are signs of contact on these but no visible wear. When I drove the same route the rattling had gone and the ride felt smoother on the rough surfaces, riding better over the irregularities.
Going back to my original printed pair, these seemed to be a half-way house. Rattles on a rough road were gone but there was a greater feeling of the road surface transmitted through the body than with the OEM rubber bushes.
Try reaching across with your left hand and pushing a couple of fingertips against the gap between the vinyl trim at the top of the door and the front of the roof well while driving on a rough road. With both the printed bushings and the OEM ones I can feel a very very slight squashing and release; about the same with both types of bushing.
My overall opinion is the plastic bushes definitely do make a difference to the feel of the car but it may be more about how much of the road vibration is fed into the upper part of the car rather than any great stiffening effect. Yes, probably minimally stiffer to transmit the vibration but not in any way enough to affect handling. I’ve now reverted to the OEM rubber bushings for what I feel to be a smoother ride.