I've been using simplify for a while now, here are my suggestions:
1) Duplicating a group should result in another group(s) not a bunch of ungrouped objects as it does now.
2) The cross-section feature should aid in selecting objects. Currently if an object is obscured by another it is unselectable in the 3d viewport, even if the cross-section is used to reveal it.
3) Option for a solid first layer under supports to aid adhesion.
4) the rotate manipulator should allow for rotation in all axis, not just z (nevermind, this feature exists, just not default behavior)