Words are cheap. They are quickly blurted out before we even get the chance to analyze how much they comport with our true feelings. We may genuinely mean it when we say Thank You, but it can sound exactly the same to the receiver whether we mean it or not.
Showing significant appreciation should cost something. That could mean monetarily, but it may also mean time or effort. Telling your superior how appreciative you are of the job is one thing, truly hustling and going the extra mile in every task communicates a different level of thankfulness.