Is this a good solid reliable vehicle to purchase or is it prone to mechanical issues?

It is hard to say if any car is a really bad coice. With the milage the car has, it has to be somewhat of a good car. What really matters is how it was maintained. I can tell you that one of the top issues that people neglect, as far as I have seen, that requires at least a new head gasket if not a full engine rebuild is the anti-freeze. Peolpe tend to change their oil and neglect it as well as the transmission fluid. So, look on the web for the NHTSA, I think that's right, website and it has safety recalls. Then check for consumer reports such as auto trader I believe has links to customer reliability reports. Reliability reports should be checked from ore than one source to make sure there is no bias. Chrysler shares manufacturing with Mitsubishi. I cannot recall what the sister car, if there is one to the concorde is. So, look into that on the web and see how the sister car fairs. You will also find information on the motor as it is probably used in may platforms. I am sorry I cannot take the time to do alll that research for you.
The last and best advice I have is to take a refrigerator magnet with you to check for Bodo and/or accident repairs. Don't put all your trust into a Carfax as a lot of stuff slips by. Purchase an anti-freeze tester and test the anti-freeze. Also, look at the tranmission fluid. Get a flashlight and even a magnifying glass to look at transsmission fluid and engine oil in light. Sunlight will work well too. The transmission fluid will smell burnt and look dark if it is old or bad. The light and magnifying lens is to look for particles of metal. That is a sign that the engine is stating to wear out and will need a rebuild. The easier the particle is to see, if you can see it with the naked eye, that is not to good, the worse the wear and if the metal is copper colored or brass that is a sign the motor is on it's last leg.
Good luck and researhing and comparing findings is the best way to go. Also note how many concordes do you see for sale and on the road? That is a sign of how long there service life is. Remember the Chrysler Sebring? A lot of people bought those and I seldom see them on the road. They are the sister car to the Mitsubishi Eclipse which was also sold in even larger quantities, but you don't see a lot of them surviving. Look around for old honda civics, you see a ton of them because they last a long time.
I hope this information helps.