Hi Brian,
I wonder why people are not using Layouts.
They are a very robust way of accepting user inputs, using them in calculations and then propagating the resulting design parameter values to parts and assmeblies.
We use layouts everywhere in a big way .... have been using them for the last 15 years, with extremely good and robust results; no problems whatsoever.
However, when you say layouts are rarely used, then how are you all automating your design process?
We have modules, wherein the user inputs captured in a layout are used to drive the whole complex assembly design - top down; it can even be bottom up.
Cheers
Shailendra