If the main difference between graffiti writing and street art is intention the what is the intention of each approach? Graffiti writers are said to be not interested in the general public understanding their artwork and are primarily concerned with other graffiti writers who can decipher the coded tags and appreciate the style of the writing. This ignores the intended public impression that is created by graffiti which can be complex.
To assume that street art is intended for a different audience still leaves the question as to whether it is really art? Perhaps it is enhanced art with the advantages of real surprise being captured.