When cleaner isn’t better

There are some circles where this is generally not true (there’s a circle around my house, for example). However, there are a few narrowly defined areas where cleaning – especially with commercially available solvents – is taboo. I’ve heard that there are families where the unwashed spaghetti sauce pot is an heirloom, passed from generation to unwashed generation. What I want to know is if the same can hold true for a coffee mug? The way I see it, an office coffee mug is barely worth it’s weight in Cascade if you can’t determine it’s age like an old tree.