Ok, my quick ideas are the following ones. It may be that this is already possible and I just suck using the editor
1) Selector Button of Blocks/Items:
in old tmuf, if you click this button you will also copy the z-Level of this block. In Maniaplanet it is for sure not the default setting and also you cannot read out the z-Level.
--> first feature would be something to get this z-Level and maybe to save it for later usage
2) UI improved z-Levelling
i imagine a UI where you can save (and see) about 5 z-Positions (and for each of the 5 you can apply them to the block/item block below or from top or from center). Maybe you can even name the 5 z-Positions. Like this you could constantly map on a specific z-Level and change it. Then go to another area and easily going back. When building with blocks the z-Level is found rather fast but with items I struggle sometimes if they have a small rastering...
3) Globally apply a different rastering to items
My ideas would be that you globally overwrite the settings of an item such that i get an easier handling by default.
4) Improved rotation management of items
A UI where you can see the rotation of the current item and you can manipulate it. Instead of just trying with the kb.
As mentioned before I haven't searched very intensively if some of these features already exist but these are the first topics and I imagine 1,2,4 would be implentable in OpenPlanet. For 3 im not sure if Maniaplanet would allow this..