For my money, it's all about rubber: tires, subframe mounts, torsion bar bushings, engine mounts. Replace these and you will see huge improvements in noise supression and feel. It will then expose other faults, if they are present, like idler arm bushing, steering box play, steering damper and ball joints. Last thing would be control arm bushings which, unless they have gone unattended by PO, should last longer than any of the above.
That said, I am still searching for the answer to a metallurgical question: Do springs get more or less compliant as they are aged/stressed. One source says that the molecular changes that happen to spring steel would cause springs to actually stiffen as they wear. I can probably till sleep without the answer, but it is a reasonable question.
g
'64 230sl, fully sorted out...ooops, spoke too soon