Here's an answer covering the more general question of calling another PS script from a PS script, as you may do if you were composing your scripts of many little, narrow-purpose scripts.
I found it was simply a case of using dot-sourcing. That is, you just do:
# This is Script-A.ps1
. ./Script-B.ps1 -SomeObject $variableFromScriptA -SomeOtherParam 1234;
I found all the Q/A very confusing and complicated and eventually landed upon the simple method above, which is really just like calling another script as if it was a function in the original script, which I seem to find more intuitive.
Dot-sourcing can "import" the other script in its entirety, using:
. ./Script-B.ps1
It's now as if the two files are merged.
Ultimately, what I was really missing is the notion that I should be building a module of reusable functions.