We purchased our Prius with 7,000 miles on it (original owner left country). It has performed exceptionally well except for the electronic issues that were repaired by removing and replacing the computer screen (Toyota covered it). Only other issue is Tires. The vehicle is heavier than most and you need to ensure that you purchase tires recommended by the owners guide to ensure that you do not risk the tire "rolling" onto the sidewall in a higher speed turn or situation where you must "dodge" an obstacle at higher speeds.
The ability to open and operate the car without "touching" a key device is a huge convenience factor along with the computer screen that relays fuel economy, etc. I love my indash map system (although it has a few quirks). We enjoy our Prius so much we now own a 2nd one (2005 model).
Leather seats would be a major improvement (much easier to clean). It would be nice to have the navigation system available for the passenger to operate while the car is in motion. You can't always pull off the road (traffic jams where you are crawling and need to find an alternate route).