I took off my wheels to install a new set of First Edition rims, and what's underneath? A lot of rust, at all four wheel hubs. I live in New England but I don't take it out in storms, it stays garaged, all that. Why after four years, and only 16,000 miles, would the center of the hubs turn this brown? Anyone else have this happen?

 

Pretty common for that area to rust, regardless of the car make. Dissimilar metals, areas that get moisture trapped. I like to clean that area and the wheel’s mating surface up with my M12 right angle die grinder and an abrasive pad. I also like to coat the mating surfaces with anti-seize.

 

If the hub is that rusty I would be worried about the wheel nuts, lots of reports over on the Pommy forum about the stock wheel nuts rusting between the caps and the shanks (they are two piece) causing the cap to swell and then break off when trying to undo which then makes it a real pig of a job to remove the nut.
Better off getting some solid one piece nuts such as Gorilla.

 

My hubs looks exactly the same.

 

I see that type of rust on most of our cars, and on other cars that I 'help' to maintain.

I like to smear a thin coat of anti seize on those rusted bits...AFTER cleaning up the hub-centric mating surfaces of course. I have had a few cars where the wheels needed brute force to remove...