- A button/command should DIRECTLY Add (an existing) object to an existing Solid (regardless of if the selected object is a solid or not).
How it currently works
After running Auto Detect Solids, any created Solids cannot DIRECTLY be "added" to another Solid (for "Visualization" only) without "deleting" the solid first (and so loose the sight of it), and then to look up the same object up again, and only then the object can be "added" to the Solid (using the button "Add Visuals". Takes too much time with big models and if need for frequent changes due to adapting the model).
I suggest to skip ALL the above, changing name of the "Add Visuals" to "Add to Solid" instead (because "Solid" is the term that you see in the UI and therefore "Solid" is the keyword that binds the "Line of thought" together. The current text "Add Visuals" doesn't explain anything to new users, it only confuses.
Explain also this principle in the help file, that *additional* elements in a Solid isn't calculated individually, they only get a free ride" with the Solid.
- In the Solid list: Make commands available on the Right Click Mouse Button (RMB) :
 "Show & Hide"
 "Add to Solid"
 "Remove" (Solid)
 Allow Direct Drag & Drop an element from one solid into a nother Solid.
More suggestions later.
GENERAL COMMANDS - TOOL PANEL
Perhaps a general "command line" edit field as a first step would be helpful in that it would be easy to give "direct access" to commands in minor releases until a UI can be made and tested.
In any case, a separate Tool Panel (which always stays up, unless explicitly closed) for the most common commands like Hide/Unhide, Lock/Unlock, Make Instance etc.
I also think that Simlab Composer would benefit from a user driven Wiki where help topics could be elaborated and explained in greater detail.