Are "dream of" and "dream about" interchangeable or is there a difference between them in meaning and usage.
To dream of something implies a want, a need, a desire:
I dream of traveling the world
I dream of world peace
I dream of Jeannie
To dream about something is to literally dream about something, and it's usually presented in the past tense:
I dreamt about winning the lottery
I dreamt about flying
I dreamt about being a millionaire
To use it in the present tense is more passive.
I dream about becoming rich
I dream about Jeannie
I dream about wonderful things.
To dream of uses a different past tense form as well.
I dreamed of having the perfect house
I dreamed of winning the lottery
I dreamed of paradise on the beach.
These have nothing to do with dreaming while asleep. They are all imagined, hoped for, dreamed of...
To speak about/of or think about/of doesn't normally have the two meanings that dream has. Dreams mean both a purely psychological phenomenon (at one end of its meaning), but can also mean a desire (as in my dream job, dream home, dream girl/boy, etc.
I suggest "Dream of" because it sounds more polite and romantic.
If I say "Dream about you" that covers the wide range of your dream, you could be flying or may get in a wonderland. While saying "Dream of you" that means being real.
Look at this example: I dream of becoming the US marine. (Internal Desire). Here you want something out from you.
I dream about a house/super car (External desire). Here you want to get something from an outside World.