I would def want to keep planar and other items no drop.
As Nilbog mentioned it brings value to completing quests for what people thought were worthless items before (not to mention quests people may have never done here that need to be fixed up).
Having a base set of planar gear with SOME resists on it also makes it so end game pvp isn't people with literally base magic resist (after being dispelled).
Wizards really aren't as scary as everyone thinks with item loot tbh (and I think the naked wizard owning everyone in PvP is a long dispelled myth by now)... provided its not level 60s sunstriking people trying to xp in city of mist (dis 8 lvl range man..) :P.
We can put this issue to rest with a flat "no" from box Emperor Rogean whenever he emerges from his training in the Dagobah system/SMS/password stuff here
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However, I'd strongly suggest putting this in with the 4 level range. Rallos Zek will smile down hard upon people buying CoFs and Trak BPs. Many Outback dinners will go down the drain. Pras.