Hello,
An excellent post.
You said,

"Only one more Shuttle flight is really needed: that to repair and
upgrade the Hubble Space Telescope. That mission should be flown
without further delay. After that, the Shuttle program should be shut
down, and its $5 billion per year budget moved over to fund the
development of a heavy lift launch vehicle (HLLV) and the other
flight elements needed to send astronauts to the Moon and Mars. The
HLLV could also be used to launch and complete the International
Space Station much more rapidly than can be done through prolonging
Shuttle operations."

Replacing Hubble's gyro's would be a fitting end to the Shuttle program. What could be better that helping to extend the life of humanity's best pair of eye's (visible light). NASA's teams do an amazing job to make sure each Shuttle mission is safe, but the Shuttle program is close to becoming just too complex/expensive for its own good.

However, large payload capacity is one of the major associated issues. To my knowledge, there isn't anything currently available to replace the Shuttle in terms of payload capacity. Could the HHLV be "fast tracked."

Still dreaming of Mars in my lifetime...

Regards, Vince