I think this is a great idea.
I was born and brought up in Marple but left for college and later for teaching jobs and only came back to Marple permanently a few years ago after I retired. When I came back to Marple I only knew one person (old school friend that I'd kept up with). As I no longer knew people who I went to school with or older people who knew my parents through their business, I found myself smiling and saying "hello" like a mad woman, to anyone who appeared to be my age or were old enough to be my parents' customers - I didn't want anyone saying that I was too rude and up-ish to speak to them!
Acknowledging people in the street and at the bus stop has led to a number of people suggesting interesting organisations in the village (sorry, it was always called that when I was a girl and it's a hard habit to lose!) or just saying "Hello" or commenting on my dress or asking where I have my hair cut.
The seat on Derby Way is an excellent way of encouraging people to be friendly without risking frightening the other person and anyone who doesn't want to chat to a stranger knows which seat to avoid.
Will there be more "happy chatty" benches in other parts of Marple?