Kudos to you, OP. I think a good portion of the amateur DIYers on this board probably do more harm than good mucking about with perfectly-functioning parts. The rest waste their money imo.
Fix it when it breaks. Check your coolant level when you check your oil (regularly). Pay attention to warning lights. If you're worried, you can buy like 3 or 4 years of AAA for what The General will tell you to spend on unnecessary parts.
Honestly, however, I would probably do the expansion tank and water pump. That IS preventative maintenance, simply because you won't get a warning light if your water pump fails and the et really is underengineered on these cars.