hi, I have a 1997 Sable LS with 192k on it. I keep up with basic maintenance, and am planning on keeping it long term. Only MAJOR expense in last 8 years was a trans rebuild, about $2000. If your 99 is not rusted out, I would keep it. it's running, paid for, well taken care of, why not? I have no experience with a 2010, but the newer a car is, the more complex it is, and harder to fix. good luck, gz