So there were no ECU codes? Did the dealership do any diagnostics that concretely points to the MAF? You might want to review your factory service manual, available at
http://www.nicoclub.com/FSM/ to see if you see any diagnostics that fits your symptoms.
It would also be worthwhile to know what years of QX4's and Pathfinders used the same MAF, so you can keep an eye out for a used but known working one in our classifieds. You can also check out
http://www.car-part.com for salvage parts. If you decide to replace it with a new one, you should be able to get a nice discount at
http://www.everythinginfiniti.com and install it yourself. It should just bolt on to your airbox and plug in... if you can change oil you can change one of these!
Heath