Just replaced both front and rear tires yesterday (thanks Bruce (Rocketman) for providing the changer, expertise and muscle). I changed out the valve cores from the installed 90 degree aluminum valve stems at the suggestion from this thread (Victor short valve cores, $1.79 for four), being careful to only gently finger tighten them to avoid stripping their threads. They appear to hold air with no problem at that tightness, but of course I'll check again after installing the wheels today. The valve stems have been installed for a year and I didn't re-torque or otherwise adjust them. I believe there's no need to re-torque something that's torqued correctly as that's the force designed to keep the threads locked into place.
Anyway, thanks to all who've contributed their ideas and opinions to this thread. It has been an interesting and valuable read.