There's an easy fix to fixing fast evaporation of your water (if your water level falls 1" between water changes, like you say just that inch can be annoying.
I purchased a new ''hood'' for my 16 gallon bowfront. There's a company out there, which I forget which makes a variety of glass/plastic top hoods to fit your aquarium. The idea or premise is simply a flat hood with a glass front and plastic rear, the rear plastic snap-ins are trimmable to fit whatever you may have going into your tank, and as a result you can trim them to go right up against whatever you may have which forms a good seal.Just make sure it isn't TOO good. Evaporation in my tank has dropped to almost nothing as a result of this, and I have no worries or fears of any of my shrimp ever doing a double spring backflip from a leaf of watersprite out onto my livingroom floor in the middle of the night. As with anything there is a drawback..and that is the hood can trap heat generated by lighting (mine doesn't generate much) and ambient temperatures from your water, giving the water a chance to heat beyond what your heater is set at. I only have problems with this when the inside room temp is about 5-8 degrees above the temp of the tank, in which case I just crack the hood.
As far as the topping off stuff...like everyone has said it leaves the toxins in the water and also allows things like minerals to build up, possibly even drastically hardening your water, but with frequent water changes it shouldn't create a drastic or harmful impact. Hope this helps.