im not a mechanic but i would wager they serve some purpose if they are there, and especially if there are some listed like what i posted above.i dont think it will damage your car or anything.
maybe worth a shot to call a dealer and speak to parts and see if you can at least get a part number and from there you can search the net. might even be able to find one at a salvage yard.
ill spend some time looking around myself and perhaps others may chime in here too..
I wonder if @cpaul can shed some light on this (casting out the bat sign )...
They allow air to pass through the shroud while driving, but then help force air through the fan when sitting still. They usually dry rot, and fall out. I've never had an issue with not running them, but it depends on your climate, use...etc.
im sure there are hundreds of titans, armadas, qx's out in the world that also have these pieces rotted or torn off and they are all probably ok. still, if you are concerned, Id just call the nissan parts depot at one of the dealers and get the part number. seems like its an easy replacement item?