The in-game documentation states that the Intelligence parameter on residents "aids in discovering new buildings." So although there doesn't seem to be any visible indicator of your progress in researching new buildings, the game is using the total Intelligence of all your town's residents to determine how quickly you progress.
Based on this, the best way to unlock new buildings would be to maximize resident Intelligence. There are three ways to do this:
- Build more shops and facilities that increase Intelligence when used.
- Get more residents (always have a house available for newcomers to move into).
- Change resident professions to jobs with higher natural intelligence rating.
Job Intelligence, from lowest to highest: