Even if "all the data" were accessible by all citizens, there would still be a massive asymmetry present in the government's ability to process that data into useful information.
You see this already today with data from census bureau, FRED databases, COVID tracking tools, think tanks, etc.
Although, if one's goal were a town or even an individual city, I bet enough infrastructure to sift the data is buildable or rentable by individuals or small groups of individuals.
It becomes an interesting world when non-profits can afford big data resources.
When they pooled their data, they were the first group to notice the military had started running flights to and from locations they didn't normally fly, and it didn't take much investigative journalism after that to discover those planes were carrying people.