I personally think the curvature of the Earth is much more important then other graphical issues
This will allow the global scope. It's not just a graphics feature, it's the very basic feature of the whole engine. I think only few engines today can do it (only Orbiter comes to my mind).
I think the graphics are not the most important, and especially, game like this should run even on older computers. But DW is really way too old (16bits ? come on !).
But even weaker GFX engine should be used to it's full extent. Good models, good textures, good lightning. There are games which look awful with DX10 effects, and some other which look well with basic features (Warrock, Q3).