Although I can say that I hate nothing more than seeing these vehicles flying for the last time, unfortunately I can see no way out of the end of the shuttle program, and for many reasons that are quite logical.
-The chance of LOCV is high enough to make an extension unwanted.
-The costs are too high, they may come back into the economy in the workforce, etc, but at the end of the day, that is government money and it needs to be rationed.
-The station, which has been the primary goal for STS for the last, 6, 7 years, is nearing completion.
-Vehicles are emerging that can offer the cargo capability of the Shuttle without the added cost and risk.
-Constructing a moon program with STS would be extremely costly due to the launch and program costs, as well as the need to create extra infrastructure that doesn't exist yet. Operating and constructing infrastructure that is shuttle-less from the beginning, would probably be far more efficient.
-There are only three vehicles, they can only cope with so much demand.
-The shuttle really failed at its goal, which was providing cheap and regular access to space... and sadly, it failed miserably at it. All the 70s moon program proposals, etc, relied on an idealised shuttle, not the realised shuttle. The shuttle fleet as they are in reality, today, couldn't achieve those tasks set out for them in the 1970s- at the very most, they wouldn't be able to achieve them well.
-Do we really want/need a moon base?
It really, really breaks my heart to see the program end. I am no American, so it does not have those patriotic connotations for me, but it is still sad.
It will be a sad day when we have no "real spaceship", and spaceflight is relegated to the days of capsules and evolved ICBMs, with the beautiful shuttles relegated to museum pieces, but unfortunately, this is the only plausible future right now...
Maybe one day we will have a similar vehicle, and hopefully this time it will work as promised. But not today, unfortunately, as the way things play out is the way they are.
EDIT:
Still sad that the STS is already the end of space planes. It was way ahead of its time, despite being build from parts that had already been obsolete at the time of the design decision.
Yeah... this "similar vehicle" will probably be a fat cone-shaped... thing, trying vainly to achieve the asthetic of 1950s Buck Rogers VTOVL concepts, while our pretty spaceplanes go the way of airships, because a bunch of guys wanted their
flight prototype to operate like an operational vehicle after a quarter of a century of technological proficiency...