I have been through the same questions, was going to get a TRD panel filter for the Glanza as I dont want to relocate the air filter etc, but most feedback about the panel filters is a minimal increase in performance. Panel filter upgrades are good if you are experiencing boost creep, easiest way to prevent this is to reinstall the standard filter box and panel filter (thats if you already have an induction kit fitted).
Best unduction filter options seem to be dry filters like APEXi and Power Enterprise, i've ordered a Power Enterprise one, god knows when it will arrive as there is a backlog in Japan, but im looking forward to getting it.
Link to my post with similar theme....
http://www.toyotagtturbo.com/showthread.php?t=21919