I would have to agree that reverence is relative. One person may reverently kneel, while another person may be kneeling on the outside but thinking all kinds of nasty thoughts on the inside, in other words, being totally irreverent. A person standing with hands raised singing “Our God is an Awesome God” and meaning every word is being reverent, while another person’s reverence might be expressed in silence. Romans 14:1-8 applies here. Granted, they are talking about the strong in faith accepting the weak in faith, but there is also an application for different interpretations of the word “reverence.”
Now as far as the Mass is concerned, certain actions or the prohibition of certain actions (kneeling at the consecration, staying off the altar, delivering the homily from the ambo, etc.) are set in stone (well, in print, but you know what I mean).