411A,
Out of a couple of thousand 747s, I can easily think of 4 that are already museum pieces (hull #1 at the MoF in Seattle, the Qantas 742 at Longreach and a 742 and 74L in Sth Africa); I'm sure there are a few more around.
So clearly more than "one or two". There are more than "one or two" 707s scattered around museums as well.
Concorde was a bit special and there were only ever less that 20 airframes made. A number were shunted to museums straight out of test. Being such a special case, it's not surprising that the 11 surviving commercial frames were not scrapped.
The Intrepid people were given (really, lent) -AD under a contract under which they undertook to maintain it to a certain level - which is undoubtedly higher than what is going on.
BA would be within its rights to remove it ('come and get it'), but it would be costly to do so; so the cheaper option is to probably make it good, where it is. Clearly however, with 4 airframes on US soil, the US doesn't value them as others might; so maybe the US should lose one.
I wish there were more than the 3 or 4 flyable Super Connies around. Good on BA and AF for not scrapping their Concs, whatever is the fate of most aircraft.