Having done some plastic casting myself I know a little about what needs to be done.
First I suspect that these parts are cast using a silicone mold so its possible that there could be little pieces of the mold that can tear free and remain on the part. This tends to be pretty easy to clean up you can rub it with your hand or use a stiff scrub brush. The silicone pieces will stretch and pull free of the part no big deal.
Spiky what you refer to as silicone in the picture may not be silicone but actually "flash" which is just a little excess plastic that ends up flowing over the edge of the mold lines/mating surfaces, its a little hard to tell from the picture.
More likely the silicone that is being referenced here is actually a release agent used to prevent the mold from sticking to the part and causing the above problem. In this case you will need to use a solvent to remove the release agent. Bead blasting may work but then again it might only just move the silicone around and not remove it, it will however change the surface texture of the part and you might not want that. As for solvents use something like a wax and grease remover they tend to be less aggressive and don't cause damage to the plastic parts. Another good solvent that I have used is made by SEM and it is a plastic prep which is used as the name implies to prep the part for paint. Also for those that want to paint the parts themselves SEM makes a plastic and vinyl dye which works quite well for this sort of application it adhere nicely and then remains flexible so it doesn't chip and flake off. It also offers a UV protection which may be needed depending on what type of material Rudy had the parts made from.
Most of the better auto parts stores will carry SEM's product line. Here is a link to their site for those that want to know more.
http://semproducts.com/Catalog.asp?prod=190Rudy when things settle down for you and you get a chance drop me a line I have a few tricks that can help remove those little air bubbles, also depending on the material these are made of you can cast them in a rainbow of colors including glow in the dark.