@Muarck,
Totally agree with the tsar. When you're writing a script, you shouldn't ask, "What would the audience like to see?" Ask instead, "What is the point of the story I'm trying to tell?"
As to your specific ghostly quandry, the answer depends on the answer to that question -- what do you want to show? Is it just a slasher flick where the important chracers are the mortal people threatened by the ghost's depradations? Then you don't need much motivation for the spook. Or is the ghost itself an important chracter, a revenant doomed to roam the earth in search of new victims to atone for some past misdeed? Then, of course, the ghost's motivation becomes important and the audience may well begin to identify with the ghost, rather than the mortals.
In either case, you have to be clear in your own mind what it is you are trying to show.