GM put them there for a reason, and I believe most new cars use some sort of spring isolator pad on the coil springs. I would think it would be for noise isolation, but again, that is just me speculating. When I rebuilt the front end of my 78, I purchased new ones from summit racing. Here is the link: Isolator
They are made by Moog and 2 are required - they are $9 each. $25 bucks total after shipping costs - not too bad.