Wacky Races isn't that impressive to me, it looks basically like Rad Racer. Completely flat ground, effects easily achieved with raster distortion techniques.
I wish people would stop calling these Mode 7, or even saying they look like Mode 7. Mode 7 means the entire ground is one big texture that can be rotated, with a bit of camera control for angles and zooming in and out, and that's it. SNES games with Mode 7 still have completely flat ground but it's noticeably more realistic than Wacky Races. When you turn, you don't just slide side to side over a road with perfect perspective. Your viewpoint turns with you and you actually see the road at a different angle.
The GB demo is both better and worse than Mode 7. It supports simulated hills, valleys and jumps, much like
Road Rash on the Genesis. It even looks like it supports some basic 3D polygon rendering, in the scenery that passes by at about 1:00. But it's still nowhere near as good as Mode 7 because all camera angles are a sort of simulated 3D - you could never pause the game and rotate the view around the car, it's always straight on or a carefully designed curve that isn't really much of a turn.