As the graffiti culture progresses with age, it gets better, a bit like cheese. Melbourne's scene really took off in the 80's. 30-40 years on boundaries are still being pushed and the skills continues to develop and evolve. Freeway signs are one of the latest frontiers with many pieces popping up on the Monash Fwy.
You rarely come across walls plastered with tags. The general rule is if you can paint something better cap it. But in this case other writers have respected the tags by not painted over it. While society hates tags, graffiti writers admire the hand style used. Graffiti is one of the only art-forms which pushes the boundaries of what is aesthetically pleasing by the confronting, product placement.