my suggestion would be to:
a) order new plates (personalised plates are fun)
b) Buy a smoked plate cover and leave the plate alone, this way you are legal and it cleans it up.
c) repaint the entire plate. It looks old enough not to have the reflective graphic on it, so get some white and blue tremclad paint and give it a sand, tape off the letters, and clean it up.
d) go to the DMV and ask for replacements, if they ask why, say you are concerned about the natuarl aging of the plates and do not want to recieve a ticket for them not being clearly visible to an officer. (this does actually work)
but do not cover the "ontario" and "yours to discover"....you can get a ticket.