Once you find a nice replacement set of brake shoes, i would seriously consider finding a used set of aluminum wheels to replace those steel wheels. I was in the same boat with a 72 motobecane for my daughter with those steel wheels with dimpled sidewalls and it was a no-brainer for me, switch out the wheels. luckily, i found an old unused set at my parent's house. there are many options to ebay.

as an example, amazon sells new inexpensive aluminum wheels from US$19 through US$47 each in 27" and 700c sizes. you would gain not only increased brake performance but also a general upgrade in cycling performance with lighter wheels. and forgive my ignorance but certainly there are yard sales or other used options in stuttgart?

eric
fresno, ca.

PS, and as FrenchFit mentioned below, these amazonian replacement rims (if available to you) are hooked, so they would allow using higher pressure in the tires.