I bought my 2004 Sentra with 10 miles on it.
I keep up with my regular maintenance (oil, tires, filters etc). The only mechanical issue I have had was a sensor went out. $34 it was fixed (by me). I now have 195k miles on my car and it still drives wonderful! Yes I have some of the simular issues that others have had, my trunk only pops with the key (I know what is wrong but haven't had time to take it appart-simple fix), the back door handles pop out on occassion. But for the price I paid for my car, the MANY road trips from TX to LA and the fact that I have 2 children under 10-I would say I have gotten my monies worth.
I still get excellent gas miliage!
The only improvements I would make is the quality of the material on the interior of the car. I have been hit 4 times since I have purchased my car - the outside of the car has done wonderful!