fwiw, I don't think laughter or not necessarily represents depth of practise, but it may represent refinement of the personality. For example, there are plenty of examples of arhats who had quite annoying character traits and really were quite unrefined, even gross, in their dealings with other people. This in no way reflected their state of liberation though. It was just a product of ingrained personality traits, itself I imagine a product of karma.
Whereas the more refined arhats had more pleasing and composed manners. Exemplified of course by the arhat di tutti arhats, Shakyamuni whose mannerisms were so refined and composed he was not even given to laughter. I suppose then at some point down the Bodhisattva path, this trait might come along as well. Sadly, I don't recall mention in the dhasabhumika sutra of what bhumi one becomes too refined for laughter at.
And even so, if Bodhisattvas appear in a time and place where laughter is a better way of responding to beings, I am sure they will do so. Shakyamuni lived in a society where this was seen as a kind of spiritual excess, a lack of restraint.