Not knowing how the reflectors were coated, I would suggest just leaving them be. Alcohol or other liquids can cause etching, delamination of the reflector coating, peeling, or other damage. Physical wiping will scratch the coating as well.
Incandescent bulbs do dim as they age. The filaments out-gas as they burn and the interior of the bulbs become coated with the tungsten alloy. For maximal output, replace the bulbs at least annually if you drive a lot at night.