G-27 New gun taken from stores and reserved specifically for dry firing. Firing pin bushing broke after about a year (a little over 18K dry fires) and the gun locked up. Mother ship replaced the slide for, IIRC, $80. Although probably not needed, the springs in the slide were also replaced.
G-23 First Glock I ever bought. Have no idea how many live rounds this hoary Gen 2 has sustained, but probably well into the five digits. Its locking block broke early on . The mother ship replaced the frame under warranty and it became my live practice gun. It transitioned to being reserved exclusively for dry-fire when the G-26 was at the doctor's. About 10,000 dry fires into its new responsibilities the firing pin complex shattered: the tip of the pin came off and the spacer sleeve broke. The channel liner survived with Continental aplomb. I think the new parts ran about $40.
I, too, keep my dry fire guns dedicated to that sole purpose. I think, Blue, it's the responsible thing to do. Of course, if I were posting on GhettoWeb.rob I'd probably say something different. Can't really comment on your springs question because I've only replaced the springs in a dry fire gun when they're in the shop for something else.