Hmmm. I feel like a salmon swimmimg upstream sometimes...
When I strip a car I take every nut, bolt and washer and have them zinc plated. Greasy, grimy, rusty parts go in, shiny, clean parts come out. I then inspect them carefully. The interesting thing is that the nyloc nuts come out looking new, including the nylon. Now I realize that it's not about looks but I have used lots of these fasteners for years without a problem. (I do cheat and use lock tight). If you think about it, in most cases these fasteners are static and far stronger than the components they are holding together. (I'm speaking specifically of the suspension items.). I really think that Alfa over designed this area for the small, lightweight cars they are used in. My point is that the fasteners are called on to perform at a fraction of their ultimate strenghth.
What really wears on these fasteners is when they are spun on and off multiple times. But unless you are dealing with a previously restored car or a race car chances are they've only been spun on once forty years ago.
I never reuse a nut or bolt (btw, never lock washers) that is stripped, galled, rusted more than light pitting, stretched or otherwise distorted . But I find surprisingly few like that. We also find very few fasteners that are rusted tight and cannot be removed without breaking or stripping. I'm not bashing american cars but if you've ever stripped a '69 Mustang you know the
difference. Alfa must have specified a superior fastener.
Which brings me to my final point: I don't think much of today's fasteners. Newer technology and materials in this case means cheaper and weaker. Just as noted, trying to find a nyloc of similar dimension these days is futile.
So I guess I'm saying if your fasteners are beat up throw them out. But i would not just throw them out because they're old. Many old nuts still have a lot of life left... If you know what I mean.