Den,
I am no expert on panels or finishing.... but, from what I have found out by talking to body shops and metal finishing companies:
You can either polish the bare ally panels with a good alloy polish, and I think Belgom Alu is the best, OR you can key, etch, prime and paint them. As I understand it, a clear lacquer will not stick for any length of time, particularly on the bonnet which flexes so much.
A good compromise, if you don't want hours of polishing is to spray the panels with the Mercedes Benz silver colour. This is quite the 'brightest' silver of all!
Good luck!
Tony Stattersfield