Not a TNG character, but perhaps Neelix fits best as the scarecrow in want of a brain. Tuvix is the story where he acquires one, only to have the wicked witch take it away.I've toyed around doing a Wizard of OZ homage with Data as the Tin Man and Worf as the Cowardly Lion. No good analog for Scarecrow though. Wes as Dorothy and Deanna as Glinda.