a) Can I get [memAvailable(%)], [cpu], etc. out of xLabel, for use elsewhere simply as those values, or as values to move/resize other xLabels; or
b) Is there a system monitoring module that will do this?

I don't know if this is exactly what you want, but Rainmeter is a great system monitoring module, if you want to consider an alternative to Label's functions altogheter.

Cerbie: search the xlabel docs for 'mz'

I swear I read through the whole thing. Really. I thought "There has to be a way..."
Thanks, so I wasn't crazy thinking "all this stuff, and no way to use it..." :)