I believe the rivets were only painted and filled on the top of the P-51 wing, but then again I haven't really researched that aircraft. How visible the rivets and dimples are on the rest of the aircraft is something you will need to check against photos. In general I make the rippling faint enough to be not noticeable unless you are looking for it. It is a sort of sub-conscious effect. If other people can notice it then it usually looks overdone, but if it is not there the skin often looks a bit bland and boring.
One other trick I use on rivets is the chipped paint rivet effect. This is where paint has flaked off some rivet heads on painted surfaces. To achieve this I make another duplicate of the completed rivet layer and turn it the BMF colour, i.e light grey. To make the chipped rivets random I use an eraser tool set like this: Maximum size (1,000 pixels in PSP), square shaped, around 40% opacity, 100% hardness and 50% density. Now I click this eraser over the layer a few times until the rivets look randomly chipped. On BMF aircraft I then delete the chipped rivets from the non-painted surfaces.