1. More WYSIWYG.

Bigger better preview display.

Should reflect scale. 1:10? 1:500? What does it look like?
You should be able to orbit, zoom in/out.
There should be handles linked to the parameters settings.
The handles should be editablein the preview window.
Tooltips showing the user what Symbols or Base Stroke pattern is where
If the user clicks on a subcomponent or component, the corresponding element in the tree display should highlight, and vice versa.

The UI should be more tree based. Hard to tell what level or component you are working on. See above.

Base stroke pattern? Point symbols? Should not be hidden in another dailog to be opened and closed.
What is linked to what?

2. Integration with Multilines. Multilines parent Linestyles, there should be a consolidated Editor.
3. 3d elements: can be used as part of Linestyles. UI should reflect that. Preview window should support pan,zoom,orbit viewing operations.