An exterior masonry industry cleaner called "Detergent 500" does a great job on getting stubborn, seemingly glued on brake dust off of old rims.

If you have extra time and a little money (about $35) Mother's 3-part system of waxing does a great job in restoring the old finishes of these Volvos. In particular, it does a great job in buying time with worn down hood clear coats. You'll need about 12-15 coats of Mother's #2 on the hood, but the finished result will look like a thick sheet of glass. And besides helping to blend in the lightening color of the front hood with the rest of the vehicle, it'll help buy you some time before having to repaint or re-clear coat the front hood.

Mother's #2 is actually more important and effective than the well know carnauba wax contained in step #3.

Using a rotating regime on the front hood and roof alone of the vehicle (one dries while the other gets applied), you can literally put down 3-4 coats of Mother's #1, 12-15 coats of Mother's #2, and 3-4 coats of Mother's #3 (use the paste wax version if you can find it) in about 2 hours. The results are simply incredible.

I actually found this advice either on this board or else up on Turbobricks, and boy, whoever suggested it was dead on.