The need for water changes is completely subjective. I doubt anyone has done some firm research on its effects on reef tanks. We replace trace elements through the use of supplements anyway. So the theory that it replenishes trace elements is incosiquential. What is possibly replenishes is nutrients like phosphates, nitrates, and heavy metals like zinc and copper. RO/DI water is a little short of staight H20! So there are no trace elements there. What water changes do do is control pH and Alk, remove nutrients, and balance water parameters. So yes...In a non-skimmed system with higher disolved and undisolved organic compounds, more frequent water changes to remove excess nutrients would be benificial. The fact that you think it makes the fish "look" happier is not concrete eveidence that it is in fact benificial. Do I do water changes? Yes. How often? Couldn't tell you. Whenever it crosses my mind and I haven't done one in a while. Do I think they are good? Well.....I think the fish look happier!
But hey, that's just my opinion, I could be wrong.