a modular marble madness type game would be at least 3 types of 3d "tiles". the cube, ramp and a sloped "corner"? plus, perhaps, a rail with separate end-pieces so we can make rails, some kinda chute we can drop into/pop out of (doesn't need to be a real hollow "tube"; we can "disappear" into one end and re-appear at the other), plus whatever fun shapes/things you can think of. same for mini-golf. there are the standards + whatever else you can think of. spinner objects? get creative
as for the spheres, isn't there some kind of geo-sphere? regardless, if there's an easy way to texture it, that's what i'm hoping for (i thought the geo-spheres wouldn't required spherical mapping). remember the craftpix 3d stuff which had a 2 color texture and diff faces were mapped to 1 of 2? we could set those and "skin" our games/levels easily with a system like that.
the point for all of it would be "easy" to implement (modular sets) for AGK.