hmmm.
here is your list with a few more items...
i would vac or blow out the inside whenever i had to get in there for another reason (not open the box routinely to do just that, unless it's years in between)...the inside power supply vents and processor fans get (gently)vac'd when you do, in addition to sucking out the loose dust... (electrostatic vacuum, naturally)look closely, smell, listen...
wear static grounding strap, have pc off, naturally...
routinely, you could vac outside power supply fan opening, floppy opening, cd-drive tray and check thatpower supply fan is working silently (stick your hand there to feel the breeze), vac keyboard and monitor vents...
whenever you are fooling around inside, when done , with cover replaced, reboot computer, test hard drives, cd-rom drives, printer etc etc (see if any cables got knocked off)
when inside, note available RAM and card slots. if you see any missing slot covers, replace them (the air flow cooling is engineered to work best with those slots covered)
keep all this and below info on maint history form attached to outside of box...other stuff:
delete temp files
delete temp internet files
scandisk (if errors, scandisk until no errors, keep eye on system, if (certain) errors continue, prepare to replace hd)
defrag
check for critical windows updates
check for current anti-virus defs
check for working firewall software (if applic)
above items do once a week say