It sounds shallow, but if you combine the graying with relatively classy clothing and nice (not flashy) jewelry, you can easily emanate a sort of "I'm financially secure" vibe. Financial security has traditionally been the male role, and so coming across as responsible and with room for others in your finances is very manly and attractive to some women.
I think you are on to something there, however since I have no fashion sense to speak of and have always been mainly a jeans and T-shirt kind of guy I don`t think I can pull this off. Besides, I wouldn`t quite say that I am financially secure either, so to give off that kind of look and vibe would be falsely representing myself to an even greater extent than dyeing my hair would.
I don`t care much for jewelry either to be honest, the Germanic Iron Cross necklace around my neck is more than enough, although I do have a nice bracelet, ring and watch for special occasions but going out for a night out on the town ain`t a special occasion so I rarely ever wear them.