> Every home, school and office should have a view of at least three trees, be in a neighbourhood with 30% tree cover, and be within 300 metres of a park

Something like this has always been a driver of my home search. I've been lucky/glad to find something, but it's always been a stretch.

But as a more realistic policy I would start with homes and with ensuring schools have a play area with plants larger than the kids and too dense to see through.

I think the secondary effects on planning are just as important: urban planning goes awry when it fails to consider livability and beauty. Livability includes walkability, non-car transportation, and parking for car-dependent transportation -- things you need to do most days. Beauty has obvious direct effects, but indirectly it also encourages people to take care of the place, and to avoid being seen e.g., as a litterer.

As policy encouraging changes, it would be good to start with environmental enhancement sections in each permit, and (if possible) to publish them before they are finalized for people to contribute proposals. This expertise is rare in developers so advice would be welcome, and providing the opportunity would probably encourage people to contribute, with ideas and perhaps funding. (There should be no provision for blocking permits, to avoid adverse NIMBY incentives.)