This is a hard one to judge how dirty it would be in real life.
From the research I did it was flown from the Ryan plant to New York where it cracked the spinner, that's why I didn't cover the tip of the spinner cause the new one wasn't, no time to do the fancy metal work on it before the flight.
here you can see the first spinner more rounded than the replacement
As far as I can see it's wheels are the most dirty.
I need to add some Tamiya weathering set - dust on the wheels and a little on the underside, but I do think it would be almost spotless
and the real one here
http://airandspace.si.edu/imagedetail.cfm?imageID=1973The yellowing on the engine cowling is a clear lacquer they used to protect the world flags, age has made it yellow.
Great little kit and gave me a buzz doing it!