The more those fan ports can breathe the cooler the system will be. I dont think taking a CD slot out is helping much but it may. Make sure the front tower air intake area around the bottom is not full of dust. Sometimes you can not see that area very well and its a perf metal grill, it depends on the tower.
The door may have holes or vents in it as well. Usually I select a tower that has either a fan on the door at the same elevation as the CPU, or has some type of intake that will assist in keeping the CPU or VC cool. Sometimes thats not an option depending on the size of the CPU cooler.
In your case, bending those slats flat and allowing as much air get past them as possible would be a good idea. If you want to cut them out all the way, thats fine. Since the mount holes for the fans are well past the cut area removing the slats wont pose a problem but the fan blades will be exposed so watch the fingers. You can get universal fan grills as I posted in that other thread. You would need 80mm for that tower.
EDIT:
Another thing too, you do want to make sure the entire venturi of the fan is open, meaning the inside smooth formed and shaped edge does not have a lip of case blocking it. The aerodynamics of getting the air out very much depends on the smooth formed venturi lip having no obstructions. Even a 1/16 overlap in that area will reduce airflow because it causes the air to swirl at the blade instead of forcing a solid 100% flow.