"They gathered some info. They discussed the info at a meeting that
may very well have been open - probably their usual regularly
scheduled meeting. (Hardly seems importsant enough to the whole city
to bother having a special meeting.)

Folks on this block were not paying attention.

The "City" probably was under no legal requirement to even send out a
questionnaire or survey to begin with.

So where is their City Councilperson, Alderperson, Selectperson, or
whatever form of office they have in that municipality? "

I agree with all of that. In most cases like this, there is no
requirement for a survey or vote by the affected homeowners. It's
called a representative democracy form of govt and why we elect
officials. Sounds like they did a survey to get input, and the OP
thinks this means they had to be bound by the survey results or give
more consideration to the input of the residents before proceeding.
It's typical to take some input, then proceed with whatever they decide
to do whether it agrees with the input or not, passing it a public
meetings so it;s legal.

The best case the OP may have is if some form of a sunshine law was
violated. What does sound suspect is that the petition was ruled
invalid and they refuse to give a reason. To try to reverse this the
best course of action is to get those affected to chip in to hire a
lawyer. To do that, I would draw up a simple agreement that obligates
all those that sign up to split the costs, up to a specified maximum,
for legal fees. See how many you get to sign, then you will have a
better idea if it's worth pursuing.