You have already read all you need: reusable launch carrier being reused extremely rarely.

An experimental vehicle turning out impractical is absolutely normal. Usefulness is exceptional. (Even the SR-71 / YF-12 was scrapped. The Space Shuttle was scrapped, not soon enough.) But scheming to keep a program running anyway is extremely common. (E.g., again, Space Shuttle. And now STS.) Coolness (e.g. SR-71) is an inadequate substitute.

It takes solid evidence to demonstrate usefulness. In its entire absence, the correct conclusion is obvious.

To be fair the SR-71 was scrapped after being in service for 35 years, a point at which there where already multiple different much cheaper and usable alternatives.

SR-71 was awesome, but its reason for existing evaporated. Once it became easy to hit with a missile it could no longer be sent on the missions it had been uniquely qualified for.