I got really frustrated using the world editor. Here are a few things that would help:
textures
more textures and higher quality (or custom textures)
the ability to rotate textures
proper doors
easily transfer the position of an object to another (without copying pasting all 3 dimensions seperately), easily create a new object at a known position
save your grouped objects in a custom library for faster reuse.
import custom object packs that would populate the library
snapping aid so you always get your objects aligned
get the color of an object displayed in the color picker tool when selected
generate 3d text in an easy way
more customizable objects
thickness selector: for example instead of 3 "arches" and the 90° pie slice and the bent "wall", just 1 arch where you can select the thickness. also applicable to the hollow tube
option to add/remove bezels/rounded corners and select how much
We don't necessarily need more objects, but more options to easily create our own.