In my opinion there is no substitute for water changes. I do mine at least 2x a month. I look at it this way. Suppose you are locked up in the house for a long period of time and there is not way out. Your wife and kids are in there with ya. After a while the air starts to take on a life of it's own. There nothing wrong with it, it's just kinda stale. Cooking oders, kid odors, etc. So you decide to spray some Lysol to "clean" the air. Is it clean or just covered up to make you think it's clean? OK all of a sudden the doors are unlocked and you run outside into the fresh air. Just imagine how good that feels to you. I think it's the same for your fish.
Also a water change will dillute your built up phosphates and other uglies that creep in.
but this is JMO