[BTW, Thanks for your help and efforts with the P4 plugin. It is a fantastic tool!]

Using a parameterized build I can set a string parameter X to a string value then reference ${X} in the Perforce workspace form where it resolves at build time to the value of ${X}.

Alternately, using choice parameters (having pre-defined values) I set the value of X in the Perforce workspace form (or view) and it does not resolve the value, but rather passes it as a literal string: "${X}".

The ability to resolve choice parameters seems to be a valuable functionality to have.