The impression is collective and the control is not
A precinct is judged as a whole by everybody who visits it. An owner who maintains their frontage carefully still shares the impression created by an adjoining owner who does not, and there is no mechanism that requires either of them to consider the other. Each is behaving entirely rationally within their own budget. None of them is doing anything wrong and the frontage still reads badly.
That is a coordination problem rather than a cleaning one, and it does not have a tidy answer. What can be done is practical rather than structural: adjoining owners who want a consistent result can align their timing and their standard informally, without anybody committing to anything. The cost of doing so is essentially nil and the effect on the frontage is immediate. It is one of the few improvements available at no additional cost at all.
