With planted tanks like that most people only clean them every 6 months or year, but they do get cleaned. Plants do a pretty good job of cleaning up the environment, but because tanks are closed (and incomplete) systems, they do need to be cleaned. Soil should be replaced, at least partially, and they drainage material will need to be cleaned , as well as the glass and plant leaves and other things that will get dirty regardless.
I know it's a drag to take it apart, but as long as you do it carefully, it shouldn't be a problem. Also, the larger the cage, the less often it has to be cleaned, but make sure it isn't so large that they can still find their food.