Humility means to think oneself as very low, and to be ready to offer all respects to others without expecting any respect for himself. Does it include always appreciating and glorifying other devotees' devotional service, without feeling that "I'm doing better service than him"?
Answer: Always Appreciate the Other Devotees
Srila Prabhupada taught us to always consider that the other devotees are more advanced that we are by addressing them as "Prabhu", which means "master." So the answer to your question is yes. We should always appreciate and glorify the other devotees and the service they render without proudly thinking that we are superior to them.