Luke's "Experienced Dreamer" ability states that he gains 1 clue token whenever he enters another OW area or Luke becomes LITAS. If Luke already possesses the maximum of 5 clue tokens (because of this Ancient One), then is Luke automatically LITAS? It doesn't seem fair to penalize Luke this way because "Experienced Dreamer" is supposed to be beneficial but I don't see any other choice but to send Luke to LITAS. Is this correct?

I think you misunderstand his ability:

Luke gains 1 Clue token each time he enters an Other World area or [whenever he is] is Lost in Time and Space.

It's a reward, not a penalty.

You're right, I did misinterpret Luke's ability. Thanks for the clarification.