It is not about reinventing the wheel.
When it comes to space exploration false economies like reusable vs. single-use vehicles should be avoided. It is more a matter of efficacy and cost.
Sure you can use the shuttle engines many times and that is bound to save some money. There are, however many costs beside the monetary. How many astronauts lost their lives during shuttle flight ops? That is a heavy cost that must be figured in.
On the monetary side, the last time I looked the cost of putting most payloads into orbit is not cheaper via shuttle. Shuttle launches are subsidized, so there is a false economy here.
Have you noticed that the military is not using the shuttle as much. Maybe they think it is too unreliable for things that involve national security.
Reusable spacecraft are in principle more economic. However, this will require a sustained development effort. The shuttle is the very first and only step in this direction.
In terms of efficacy, it seems that NASA has chosen an approach, using throw-aways, that has been historically more reliable. This way NASA will at least have a program.
The best use of funds is the use that succeeds!
We are no where near the point were we can gas up the space ship and shoot off to Mars. Space technology is NOT a mature technology.
