I had a CD250U. Discovered Dave Silver was selling off the last genuine exhausts for about £100 a side, bought a pair, stashed them in sealed bags, and they went with the bike when I finally sold it. Buyer was delighted.
I have a CB Two-Fifty as the commuter steed now: bought it for £500 in May, with just £12,000 miles on the clock. Same bike, except (oddly) it has a single carb head whereas the CD had twin carbs. The CB is extraordinary - no faster, but it does 85mpg and will do 275 miles before reserve kicks in. DS was also selling NOS exhausts cheap, and I bought a set: £89.95 a side +VAT (and the clamps and gaskets). I'm thinking of buying a second set, as before, and just salting them away.
As you do.