My DD is a 2004 Grand Prix GTP car, 3.8L engine with a S/C that I have owned for many years and the last 160K miles (coming up on 200K miles) almost are all mine. My quick review.
Overall nice car to DD easy to see out of and park, no one (including the police) seem to notice it, looks nice in most areas, handles well enough to pass many other "nice cars" on the road and on ramps, paint is holding up well, inside is not doing bad (some buttons are worn), factory radio and speakers sound nice, and has been reliable as gravity but has taken some work and money to keep it on the road and I know the "BIG one" is coming.
One of the things that caught me off guard was the amount of light bulbs this car eats, like potato chips at a football game.
Oil leaks, just fix the big one's.
Change the SC oil every 50K miles
Flush the cooling system every other year.
Coolant tubes last about 65K miles
Outer tie rods last about 80K miles
Hub bearings J.F.C , around 178K miles three of these berkeleyers checked out within 3K miles of each other (one of each for noise, play, ABS) and good hub bearings are not cheap. The fourth one seem to be hanging in there.
A few say what repairs:HUD spring, thermostat (EVAP code!), and wheels. Yes wheels, the factory wheels leaked air, in the winter I did not mind (twice a week) but the summer I was putting air in at least once a day sometimes twice. Save you time and money just buy new ( non GM) wheels.
This is not a complete list but some of more expensiveness and reoccurring repairs.
According to the interweb the 3.8 eats head gaskets, intake gaskets, water pumps, radiators, steering racks, and drive belts like candy. All of mine are original.
The "BIG" repair will be the transmission as after you drive for an hour or more and come to a stop the car takes about four seconds to engage first gear with a nice little bang. This started about 18K miles ago but seems to be occurring more and more, this maybe where I get off.
Overall I have been please with the way the car drives and has held up over the long haul, I was coming off my third in a row foreign turd and just needed something that was not going to leave me on the side of the road/ parking lot/ my driveway for the zillionth time in three years, no tow truck for this car. Good car for the money and I have seen a few nice ones for around $3K.
Paul B