The Idea: A website where residents can submit ideas, vote on them and donate to improve.
Deep Dive: You could build this one without city administration buy-in. Giving residents the ability to add, vote and donate to improvements could be enough to fix the issues or make the improvement.
Once you have some traction with votes and donations you could present the data to city officials and they would be more likely to make those improvements or fund the rest of the bill for items.
Validation: Local volunteers ask for donations for our local park all the time. These are volunteers that use that money to buy trash bags and pay sanitation workers to remove the trash.
Monetization: You could take a small cut from the donations that are implemented. Once you have traction you may be able to receive some grant money from the city to help operate the business.
Backstory: Every city needs local improvements. As much as I'd like to blame the administration for lack of action, it's nearly impossible to locate and fix every problem and build the right improvements. Giving city residents the ability to vote and add improvement ideas would help bring to light any city issues.