I have driven my Prius over 100,000 miles and have had no repairs!!! (just new tires and oil changes) This have been the most reliable car I have ever owned. THANKS TOYOTA
Mine past 117k+ miles still on the original set of brakes, 3rd set of tires. change the CVT fluid at 85k miles, changed the spark plugs at 105k miles, recently change coolant for the ICE and inverter. That's pretty much it beside the regular oil change, filters change etc.
I would think by 100K miles, you should change your spark plugs, brake fluid, coolant, trans fluid, etc. (We did all this on our 2005 when it went over 100K) Still, these are very economical cars to maintain. Trouble free.
Dealer told me spark plugs at 130,000 . But I do need to do a coolant and Inverter change and trans-axle change.
The sparkplugs looks fine even at 105k miles, but the coolant is needed for the ICE, the inverter seems fine but I changed it anyway. Dealer will charge you twice for the coolant, since they consider the inverter is a separate coolant system. The spark plugs change isn't easy, you need to remove the wiper assembly/motor/tray in order to access to the ignition coils/spark plugs. It's time consuming. here is the youtube video someone post it. hope this give you an idea.
I've never changed spark plugs in any of my cars and they still all run fine. I have Ford, GMC, and Jaguar. Ford is at 250,000 miles.
The spark plugs will eventually fail -physically-. If that happens those wonderful ceramic parts fall into the engine. The piston isn't impressed. It won't be warranty. Go ahead, leave them in too long if you dare!