1. When an input or output connector on a block is selected, the connections from there to other blocks changes from green to blue or yellow as appropriate. (This would make it easy to check connections in complicated layouts where connections are sometimes hard to separate.)
2. Snap to grid option for positioning blocks on the canvas.
3. Ability to select from a few alternative colours to the standard grey on individual blocks. (Not for cosmetic reasons, but to make blocks more easily identifiable in complex layouts.)