Really good ideas so far. Especially better physics, more interesting looking planet surfaces (they should invite you to explore the celestial body), better graphics and I like the idea of cities ( at least some lights that show up on the dark side of Kerbin)
I would like to see a scaling option for fuel tank lenght. Stacking them feels a bit inconvenient and often looks ugly (I'm a sucker for nice, clean and simplistic looking spacecrafts, a bit like their real life counterparts:))
That's all I can think of at the moment:)