yea theres lots of different theories on weather or not to change water, my dad was a big "dont mess with the mix" kinda guy, and while i totally agree with him on a glass of sweet tea, i have to dissagree with it on a fish tank...
I dont know if water gets "stale" like air in an old house will, but i personally believe that changing the water is the one thing that i can do that will make the biggest positive impact for my tank.
even if its just 10% a week, or heck even if its every other week, if your not monitoring all the different elements, then dosing for them, then you have to do some water changes or sooner or later it'll catch up with you and your tank, and the results may not be pretty..
just my 2 cents worth tho...