For Sierra games, I'm very grateful they fixed the bugs because there were so many, especially in Quest for Glory III and IV, which are some of my favourite games ever.
For legacy SCUMM games, I agree that adding a toggle to switch between versions is a good idea. Then again, I personally never encountered bugs while playing any of them and often thought that the code behind these games was error-free (but reading this thread certainly highlighted the fact that it wasn't).