Derek Clarke wrote:
So the obvious approach is a two-stage one - fly the wings and
atmospheric engines away once they no longer serve a good purpose.

The problem is that the optimum staging speed is about 3km/s. But the
wings are normally only good for maybe mach 3 or so (1km/s); after that
structural heating problems start to really get interesting.

So you're compromising your first stage when you stick wings on in
several different ways.

Spaceship One on steroids...

Yes, but it might be observed that Spaceship One took two stages to do
what one stage can do. Even Rutan admitted that a lot of the tech he
used was because it was stuff that *he* knew how to do, rather than
because it was inherently better (but he did have some good ideas, the
pivoting tail structure seems to be a reasonably good idea.)