750 Commando Crankshaft reassembly hardware question: Is new hardware really needed?

Yes - I believe that these critical fixings (crank assembly and big end) should never be reused.
If done properly they will have been torqued to proof and, as such, their life is spent.
New bolts and studs here every time in my view.
You are entitled to your view. Norton and later AN agree with your view for their crank hardware and rods.

I have Carrillo rods and follow their advice for rod bolts. Rods with nuts would have a different recommendation.

Steve Maney gave different advice for the hardware fitted to his crank. Since I have a Steve Maney crank, I asked for and follow his advice. If I had a Norton/AN crank, I would follow theirs.

If I had a Molnar/TGA crank I would ask them, and if I had a billet crank I would not ask anyone! :cool:
The thing to remember about the case of a Steve Maney crank, as I have referenced, is that the hardware used is not standard AN. So there is only one source! Steve is very particular regarding tolerances, both or the cheeks, flywheel and fasteners. Fasteners are properly sized to fit the holes he has bored.

AN hardware will not be adequate for a Steve Maney crank, and indeed it is different between different Norton model cranks.

Ergo, unlike the Norton case, where changing them is indeed a cheap insurance, you need to do what the manufacturer recommends.