Q:

"Cast a spell on people" vs. "cast a spell over people"?

What's the difference between the two? Example:

She cast a strange, yet beautiful spell on people.
She cast a strange, yet beautiful spell over people.

A:

Over can imply that people refers to a vast crowd of people and that the spell is cast upon all them as a whole.  This further makes the sentence possibly imply that you mean something like where a speaker "casts a spell over" his/her audience.
On would tend to imply that the effect is more about "any person" or individual people.  

