The ‘Style’ is that of a ‘Graffiti artist’, not stating that the art is in itself, is uninvited Graffiti. Point of fact, there are many ‘Graffiti Artists’ who started out as the typical ‘Graffiti Punks’, but due to the nature and skill of the pieces that they did, the property values actually increased, and these people were able to cross-over to legitimate artists.

The problem is that many have something that they want to express but have very few actual outlets for them to do so. As with all things with practice comes skill and subtilty, unfortunately there are too few venues wher graffittists can express themselves without causing the very damage that you are talkning about.
If there were venues that allowed them to practice, perhaps with non-toxic water based spray paints, (so they would have fresh surfaces after every rain) this might not be as much of an issue.
In some cases, the artist might prefer the temporary nature of the graffiti that they aint with these paints.

Perhaps this is too hopeful a thought, but it alsomight be a viable alternative.