Research point - Street art

This is something that attracts me. I visit London quite a bit and I always look out for it. The suburban town that I live in has fewer examples, I did some online research to see if there were any that I have overlooked or forgotten about. This council sponsored street art doesn't even credit the artist.
The town has a canal running through which is an obvious target so I took a walk.

This is set by a lock. It's too clever a design to call it graffiti but its not a particularly sophisticated example. The swirling shapes reflect the way the water flows through the lock and maybe the bottle top has something to do with there being a pub opposite. It's also quite likely that I'm reading too much into it and its just a tag done for the hell of it. The swirling style of the shape is similar to other examples on the towpath.

This is just the other side of the bridge that has the first image on

and this is a bit further down. I feel that graffiti artists get some joy from the sweeping arm movement required to make this shape.

This is another example from a bit further down. I can't see any connection to the surrounding area but its a well executed piece with a feeling of three dimensions. A more finished version of this one so that probably classifies it as a tag rather than art.

Across from the canal on a semi derelict building that is close to the railway line is this.

Someone spent time and effort to get this right. Although it appears empty at the moment, the building has been used as a squat and I guess that the mushroom may be a reference to the activities that took place in there? I don't think that it looks like the same artist, The other examples have a more restricted colour palette.

This is further down the canal close to the historic Apsley Paper Trail. It's been there for more than 10  years and is starting to flake. Although its done in a graffiti style I suspect that it was council sponsored although I can find nothing to confirm this. It seems rather reserved and self conscious and it's been there so long without being removed.
Up the hill away from the canal I've seen variations of this tag in several places.

It seems to have no connection to the places that it appears so I think that it is just a slightly sophisticated tag.
Is there an evolution process for graffiti artists who start making simple tags and progress to more thoughtful artistic pieces? Does that mean that they move away from suburbia to mix with other practitioners? How do they make the transition to accepted artists such as Finbar McHugh?
If graffiti artists evolve is there a difference between vandalism and art? Every sketchbook has examples of things that didn't work out or ideas being developed, I don't think that it is realistic to tolerate everyone using the walls as a sketchbook and the vast majority of what is graffitied is just vandalism, but for "artists" you probably can't tell if something will work until it is in place. I don't make good art if I'm stressed (by location or the interest of bystanders) but do street artists make better work by being in a rush? Is it about a different personality type?

Guardian discussion of street art here. A friend sent me this story about an accidental piece of official graffiti art in Australia. (I don't think that Phil Hoy is a relation....!)

It's corporate commercial art but I was amused to see the hoardings outside Euston Station.

Which has a resemblance to drawings that I did for Drawing 2