It would be very helpful if other buildings in the same category as the one you are about to build - would light up or be marked on the map somehow.

Maybe just color the building blue and show an icon above it.
For instance when you want to place down a Clinic - have the other clinics which you already built - stand-out among the other buildings.

This will help you in city planning so you do not end up with a clinic around the corner of another clinic.

This should also be shown like this when you use the Healthcare Quality and Coverage overlays.
Right now it seems to only give an icon above a clinic if the wait times there are long, but no icon if it is not under stress.

EDIT: Same principle applies when selecting a building, for example the Newspaper.
Why does it not show me where my other Newspaper buildings are?

When a city becomes larger - it can be quite hard to "remember" where you placed a certain building.