So I recently discovered by way of an anon in /lego general/ that Pledge floor polish makes transparent lego elements shine. The floor polish is able to adhere to the polycarbonate that the transparent elements are made of and fill in all the little micro-abrasions and cracks caused by the parts knocking against other lego elements, and clears the ‘fogginess’ that appears on older transparent parts. This does not work with regular (ABS) parts.
All you have to do is make sure the part is clean of all debris or discoloration, dip it in the solution, and wait for it to dry. Word of warning though, the thin coating added to certain parts may make connections have stronger friction than transparent parts already have with each other. It varies a bit from part to part and connection to connection, but other than, say sticking a lightsaber rod into a transparent cone, you shouldn’t have much trouble.