I have seen examples of TSC files with enumerated [elements] and with 
I assumed the scenery loader needs to merge [element] entries from multiple TSC files into an internal list anyway so enumeration does not seem
to be particularly relevant. Since it works without enumeration I did not bother to add it.
As for the [autoheight_override] I am unclear on the interpretation. I forget where I copied the original snippet for the template but it did have [-1]
Models I have placed at zero elevation in Sketchup seem to render at grade level with it set to [-1] (or  ) so I left it at [-1]
For an object model with larger area, if there is a slight slope in the elevation data one edge may be floating or depressed.
I had to extend the pylon piers well below grade to avoid floating pylon legs on steeper grades
If [autoheight_override] is set to  only XREF objects will render (no user defined objects).
As with the element index the autoheight_override did not seem broken so I did not fix it.
Changing the default values is easy if there is a "correct" answer.
Adding an optional model configuration element is more work so I would need to see good justification for the change.
The models I have converted worked fine with a zero elevation in Sketchup and autoheight_override of -1