Of course, one of the favorite factoids that I share with visitors is the different color of the marble of the Washington Monument showing where the construction was stopped. Construction began in 1848 and continued until 1854. When donations dried up, the construction stopped. When construction resumed years later, the quality of the stone and work was so bad, marble was later removed. When construction resumed in 1879, it was impossible to find exact matches for the marble.
Personally, I think that they should leave the scar as one more interesting record of the monument. We all have scars to brag about.