Show plates can be really great looking (get to a place cover your plate with a cool show plate then take off when leaving) but road legal is road legal and I think anything different on the roads is just stupid. Also Black heritage style number plates that match your car's colour schemes etc and these can look brill but these are also illegal. What about wheels and tyres that are so offset they protude from your wheel arches they look "cool" too! (Illegal but "cool")
Like Chris or Helen (Hi!) say you might as well get the front limo tints to go with and just waste the money cos you'll have to get them removed eventually, when the police will stop you.
Being Road legal is a massive part of being a responsible road user. That I respect.