Not sure which ISM told you that compliments don't mean anything. In the numerous times I write compliments, the crews are overjoyed (including ground crews, when I also offered to write them compliments, they are overjoyed). I asked a few times do these compliments really help them, and the most common answer is "during performance reviews and promotion reviews, it makes a difference".
Keep giving away the chocolates or gifts, but do not discard the power of the pen of compliments.