It's impossible to really measure how and how much something achieves in the long run. Not that I want to compare this defacement to that, but just to point out the impossibility to measure such things: does the photography of James Nachtwey help to improve the world? I'm thinking "of course it does, there is no way it doesn't", but nobody can know how much.

If this made just 10 people reflect a bit on stuff they otherwise wouldn't have reflected on, how much trouble and costs would this have to cause to not have been worth it? Everybody fuzzes this kind of "math" for themselves based on their perception and biases, there is just no clean, objective way to go about it IMHO.