I suspect some of the always use new spokes harks back to the '70s-80s when a box of 100 chrome plate or stainless spokes could be had for $10-12
and if you went with unplated straight gauge perhaps $7 or so per hundred (remember Union spokes from Connecticut?). Now spokes are sold per
wheel at 10-15x the costs of yesteryear. Of course a full Campy bike then was $250-500 depending on which Italian frame maker was selected so
maybe the cost is proportionate.... (which I doubt).
I remember spokes at that price and still have boxes of DT spokes in the attic but I seem to recall the best prices on a Campy Grouppo at $500 and never getting a full campy bike Columbus SL/SP framed ride for under a $1200.
DT double butted competition spokes can be purchased for around half a buck each and unless the old wheel had either DT or Sapim spokes AND the new hub has the same dimensions AND few had broken, I'd replace the spokes. When spokes start to break, like the bad apple in a barrel, others are affected. Some spokes get over tensioned and then others are not in tension at all.
OP....given how little you know about wheels, spokes, hubs, flanges, etc., do yourself a favor....get the wheels built professionally with new spokes and safe (sic) yourself