A booster stage solves exactly that. I noticed in the launch yesterday that the booster was a hog - it was bigger, but it also had a lot of engines and a lot of

A booster stage solves exactly that. I noticed in the launch yesterday that the booster was a hog - it was bigger, but it also had a lot of engines and a lot of work to do, so it burned through its fuel faster. This particular configuration is set up for the separation to happen pretty high, but one can imagine different configurations as well - a bigger ship and a smaller, fuel only booster that works only as long as there's atmosphere. Or even better - keep the current setup but have a ring of air breathing engines in the booster that work as long as they can. There's a lot of stuff some extra engineering can do, given enough time and resources. For now, SpaceX is going for the biggest bang for the buck, and they have a very healthy aversion of complicated solutions. But in time, adding a few air breathing engines may become simple enough to be worth it.