The only technical reason (technical not economical) Concorde doesn't fly anymore is because the type certificate, aka the airworthiness of the aircraft, was surrendered by Airbus, hence grounding all the fleet and making it unlawful to fly it.
So to fly it, they would need that to be reinstated.
For the Avro Vulcan, they went through a different aerospace company for that.
I'd love to be wrong, but I doubt Airbus would let anyone fly one of its Concorde...
That does not require manufacturer support, it's similar to US Experimental classification. But it would not permit carriage of passengers.
Concorde wasn't $400 more than an equivalent flight. It was >$11,000 more than a similar comfort premium economy class seat, and that's after the British government had underwritten the losses from the design program (around $2000 per passenger per flight in today's money)
FWIW, the full economics must note that people with a lot of money are more likely to hop on a business jet and get point to point service. When Concorde was designed, business jets that could fly non-stop between US and Europe had just barely entered the market. (The Gulfstream GII, May 4, 1968 vs. first demonstration flight of the Concorde 2 March 1969.)
As to your question, it rather depends on the cost, doesn't it?
To start with, it saved about 4 hours on the Paris/NYC connection, not "an hour or two." If it were only $400 more to save 4 hours of overseas travel, then many would jump at it, and find it a real advantage.