My uncle gave me that same look when I was cleaning up an old adjustable wrench. Spent twenty minutes getting the rust out of the threads, and now it works smoother than his new one. @tessa177 is right, that feeling when it finally clicks for them is the best part. They just don't get the satisfaction of bringing something back to life.
Honestly, that look is so common. Next time, hand them the tool before you start. Let them feel how rough it is, how it barely works. Then, after you're done, hand it back. The change is something they can actually hold, and it shuts down the "wasting time" talk real fast. It turns your hobby into a clear before-and-after they can't argue with.