Yes, I try and replace as many nuts and bolts as I can while I'm working these days. The time I must have spent lovingly rehabilitating old ones when I was young. Wire brushing, running dies down threads congested with rust and old paint, picking up discarded nuts and bolts off the ground in scrapyards in the hope that they'd come in useful one day. I even used to buy job lots of secondhand ones off a firm called K.R. Whiston in New Mills, Stockport. Long gone now of course.
Nowadays for safety or stress critical areas I just order them by part number when I get the bits and pieces for a job, or for non critical areas I get a bag of 50mm by M10 or whatever from Ebay or Screwfix.
I do miss all the threads you used to get. Whit., BSF, UNF, UNC, BA, and all the odd ones that were specific to a particular manufacturer.