Is this needed ?
 

I took out my old airbox a long time ago and have a AEM CAI. I'm wondering if the bottom portion of the tray needs to be left in or can I remove it for good ?

It acts as a heat shield for your intake, and a sweet place to put nuts and bots when working on your car.

I left mine on, even though its ugly

I wondered if it acted as some sort of heat shield or to help with air flow control. Agreed, is very ugly would like to find something transparent so I can see my new mishimoto radiator and fan shroud.

make one out of clear plastic

May have to look into that.