It's not something I would personally do.

I can just about see a reason to do something like this if you were flying on Christmas or New Year's Eve, to recognise the fact that crew are spending that time away from home. But I haven't yet been in the position to determine whether I would actually follow through on that.

My philosophy is a better way to 'treat' cabin crew is to be kind, polite and (time permitting, and they are open to it) a bit of chat and banter at quieter times of the flight.