I have no opinion on whether the car is a good value or not...
However, I don't understand three vehicles for two adults, other than the car was inherited. Personally, I would swap the Highlander for the Prius, as this is the greatest change in fuel economy. A private sale would probably net you a better price--and you're a mustachian so you're not afraid to get you're hands dirty. Then, craigslist the car. This leaves you a high fuel economy vehicle for road trips, and a van for carrying cargo and such.
As for when you travel, leave the unreliable car at the airport, as it is not critical that it starts every day.