Besides lower hdd temperatures, are any other advantages in an good airflow case (like 3700AMB case, with good wire management)?
None that I've ever seen.
Isn't enough only one 120mm fan in the back?
Almost certainly, unless perhaps if you're running a bunch of HDDs and a very hot vidcard.
That said, it really
does help to have some sort of fan blowing air on the HDD(s). Even a tiny bit of air cools the drive down quite a bit. I'd plan on putting some sort of fan in front, even if it was along the lines of a 5V 80mm Panaflo L1A.