I agree that player-created parks are a different topic entirely; it's even marked on the radar for the future roadmap after season 4, I guarantee they have a team testing dev there.
With the current parks, a voting system would allow more direct statistics on successful street or transition setups, most user-preferred objects, etc. Like DigitalWolf333 said, it's possible they already have a similar system in place undercover. It's easy in an engine to track player position, objects used, and time in community parks.
That being said, there are many who wish to see the game fail because they aren't patient enough or want something entirely different. Player-voted polls can always be griefed, and this could possibly hinder focused development at this point. If half the votes are made as a joke, it could heavily compromise genuine player feedback. There are plenty of examples of this over the years, and with the tumultuous feedback so far on the forums, I'd almost expect it at this point.
Perhaps a system could be established in which votes are weighted based on player trust, or a way to distinguish joke votes from real ones?
Love your idea of voting; balancing it, in my opinion, is the bigger issue.