I agree. I have used glass tops in the past without issue, as long as I cleaned the glass regularly, as you indicated.
My current tank is free standing (not against a wall) and everything, including the sump, is in the stand. I went with a sump that is covered to keep the moisture levels down in the stand, especially since I have the electrical equipment in the same stand.
I can report that the skimmer alone can provide sufficient gas exchange. In the winter when the house is colder, I use the glass tops to cut down on evaporation into the very dry home environment. However, in the summer with the house warmer, I switch to the screens to help keep the tank cool through increased evaporation and air flow over the tank.
Conclusion is that you can use either solution to cover your display adequately. As to cost, I would say that the screening kits are significantly less than the cost of a glass top, especially as you get into larger tanks.