Terence,

I vaguely remember the idle smoothing out very slightly with the AC on, but at the time our AC wasn't working very well, and we almost never tried to use it.

I doubt you'll have to replace all the plug wires, just have them tested per above, and see if any of them are bad/marginal. I don't have any experience with electrical contact spray, so I can't offer any advice on that one.

anthony