I'd hate to see another multi-year suspension of flights. I think they need to address the tile-fix-in-orbit problem, and do something about the insulation, but I think the remaining shuttles are very spaceworthy now.
Face it, few people drive cars older than Columbia was.
I have discovered a few interesting things about Columbia.
It was the oldest f course but was also the most problem ridden. The left wing heating and left side heating problems are mentioned early in the program. Special equipment and cameras were once installed to observe and correct it.
Also, the tile arrangement was different on the trailing edges of the wings.