I think you have to look after crew on staff travel if they introduce them self. Is not only about upgrading, sometimes, just a complimentary drink or something extra will be good, as it could be you, next time.
However, I always bring chocolate to the operating crew when flying as staff travel, going on holidays or just a short break (not if possitioning for the company, sorry
). I think is nice, and as you have saved money on the ticket, why not spend a little on the colleagues. At the end of the day we are all on the same boat!!
