How many graffiti artistes have been arrested more than 3 times? How many of them are serving life in prison without parole?
Clearly not enough of the vandals.
So you wanna pay for their incarceration for the rest of their life - I would rather charge them or their parents for the cost of materials and oversight and then make them all do the job - far more cost efficient, constructive and has the benefit of the whole community seeing the lesson and not wanting to end up doing the same!