I cant help but think the wall issue is a bit of scapegoat for an area that is totally and uniquely shit as a public space in our city. The focus on the wall is taking away attention from the much more important problems with the area.
I'm not saying the wall is brilliant, but to me it isn't the terrible construction many believe. It without a doubt serves a purpose.
Look at the area, on both sides are busy transport exchanges. The idea of the wall was a superb one, and even if you think the construction in it's self is vile it's hard to argue that it doesn't serve a purpose, and serve it well. It acts as a very clear and effective boundary between the tram/bus stop and the public space. Just standing on either side of the wall will give you an idea of how effective it is, the noise difference alone is noticeable. Again, I ain't saying it's a good solution to the problem, I ain't even saying I like it. But if we insist on having a public space there then some sort of segregation is needed. And does anyone actually remember the wall when it was clean? It wasn't attractive but it wasn't ugly either. Years of little to no maintenance has ruined it, as can be said for all of the gardens.
I genuinely believe that if you got rid of that wall, the place would be even worse. The miniscule sense of segregation that is needed to create a successful urban park that we currently have would be gone.
But in my opinion, the entire area just isn't suited to a public garden. It has some of the highest footfall within the city, it's almost always busy with people simply passing by - none of that lends it's self to a public place. Look at the other (shamefully few) green space in town, none of them have a significant footfall and don't really act as a central point to the area. Where people stop and relax is generally cared for, people don't show the same respect for places they simply walk through, unfortunately. I agree the wall needs sorting (despite my opinions on it serving an important purpose) but the wall is often focused on as the main problem, but the entire location, design and upkeep of the gardens is the actual problem here. Just look at the state of the grass, the paving, the benches (all of which have been 'fixed' recently) and don't even get me started on the fountain, which takes up all that space but seems to be in a perpetual state of knackered.
It's easy to say 'well lets green-ify the wall', but the MCC can't even keep the bloody grass and fountain alive, people have absolutely no respect for the area, how long do you really think a nice green wall would last? I'd give it 3 months. And before anyone says 'well maybe people would respect it more if it wasn't so shit', it didn't work with the old sunken gardens nor did it work when the area was renovated.
Like I say, the area just isn't suited to a public space, it never has been and while the transport interchanges are there it never will be. The MEN, petition and some comments on here seem to be viewing the gardens through rose tinted glasses. Make no mistake, it's always been shit. Don't be fooled by some pretty pictures that were taken on a lovely summers day after a good clean up.
If anything, the old sunken gardens were even worse than the current ones. They were out of sight, full of doggers, prostitutes, drunks and drug abusers. Both of my parents actively avoided going into the gardens at any time of the day in the 70/80/early 90s. At least it's only full of the above at night these days, for the most part.
Like I say, Piccadilly gardens just isn't going to work as a gardens. It's too busy, too many people walk through it, too close to transport exchanges. It hasn't worked as a gardens for at least 30 years. Look at the plans for St peters square, I think similar plans for here would be far more suitable. It could make an OK square, but it'll never be a good gardens.
One last comment; I think the problem with Piccadilly gardens is a great example of what Manchester (and other UK cities) are doing so, so wrong when it comes to urban green space, Here is a post I made ages ago explaining my thoughts.