having two fans in a case is standard for the new ones. Ideally, the back should be blowing the air out while the front fan sucks it in.
Me? I just open the case and stick a 16" electric fan on it blowing air at the number 2 speed.
No more worries about airflow.
Dust worries? The case fans will just suck them into the case anyway, and in most cases the dust suck in will just swirl around the case and settle in every nook and cranny all the same. An open case won't let the dust settle on the mobo and stuff... it'll still get dirty (depending on the air quality of your town), but IMO not as much as a closed one.
__________________
"...And when I finally meet you again, I want to ask you - have you found what you were looking for? Because that's what I felt you were doing, all these years. And I want to hear you answer, "Yes, I have, thank you for asking," and we'll be together again, until the end of our days..."