Yes that also reduces the space in trunk and I never use those tools and spare either, bas Allah bachaye. Someday I'll put the space saver from my car into the other car which has full size spare, just to see if it becomes flush with trunk floor and that styrofoam can then be removed.
As regards sound proofing, it always seems as though a lot of sound is coming from the trunk. I did a half hearted project in my CL9 with the objective of keeping the cost, weight and effort low, as CL9 is relatively quiet to begin with. I only did the wheel arches, trunk and door window linings. Used a combo of cheap lightweight sheets from AliExpress, 3M heavy sheets and acoustic tape. Made a noticeable difference especially sound coming from the rear. Downside is that you really dont get a sensation of speed and acceleration due to it being too quiet.