Home decorating tips have long utilized illusions to enhance and optimize form and function of tight quarters. Take for instance drapery applications in a standard bedroom with the window set in the middle of the wall. When flanked by floor-to-ceiling drapes it gives the illusion of a wall of windows, which in turn translates into the room having the sense of being larger and more open.
By taking it a step further, why not employ the same idea with doorways and closets? Traditional doorways in a 12x10 room typically are just under seven feet high -- mere inches above a grown adult's head whereas a ceiling-to-floor doorway increases the headroom by at least a foot. This gives the illusion of higher ceilings which translates into a feeling of more space. Other ideas include adding a transom above an existing doorway, swapping out solid doors with a glass French door or even installing a sliding pocket door to reclaim swing space.
Skeptical? Consider how as a small child you established familiarity within your space i.e., childhood home, treehouse, grade school classroom, etc. Do you recall thinking that you remembered these spaces as being much larger than they are now that you are an adult? By changing the threshold heights of doorways you are able to influence the first impression as one enters into the room. Why not implement some of these ideas in your property when considering making a change?