One thing that I did was to become a member of my towns "Tree Commission" which is a mayorally appointed position that reviews developers plans and makes recommendations to the local planning and zoning board on changes that should be made to have them become a more tree friendly plan.
This has involved the creation of some new or, changes in, statutes as far as the size of planting islands in parking lots, and the width of the green space between the curb and sidewalks. This has gone a long way to altering the look of our town. We also had written into the books that developers had to plant one shade tree for every 10 parking spaces and there could be no more than 16 spaces between planting islands.
It won't be easy, but with patience it can be done. Getting town officials to think in terms of 50 - 100 years into the future is the toughest. Politicians are perpetually short sighted. Just looking forward to the next election. Never concerned with the long term health of their community.
Like you, a good portion of our business was correcting the errors of the "Landscape Designer" or "Landscape Architect" types. I don't regret the work, but I would have preferred to have been doing something else. Some real tree "care" and not just removals. One of the worst we had to deal with was an internationally recognized landscape architect that was brought over from England 4 times a year at one of our major clients. He over planted on a major scale. OK, yes. The plantings did look fabulous right away. Grand scale. Huge statements. But within 2 - 3 years the trees were running out of growing space because he had specified too little separation between plants. Then the question was, prune or selective removal?
This L.A. thought nothing of planting 6" - 8" DBH trees, sometimes larger, at a huge expense, only to have some removed in less than 3 years. He selected specimen trees from all over the globe. But this is another issue. Properly selected native species plant material inherently does better with less maintenance.