Basic A+ training will tell you that the case is an important part of cooling and that the air flow across the boards is important. Removing the lid basically makes your case fans a waste of time. Therefore, the other boards in the computer are not getting air flow and are not being cooled either. So, why remove the side of the case
Dust is going to build up no matter what. You just need to clean more often!! Believe me the desert has enough of it!