The squeeky wheel gets the grease. Report it even if it just online. You have to understand that because of budget cuts, most departments allocate the limited resources where they are needed most. Since a broken window is a low priority, most departments will not send an officer out to take a report. You may have to come to the station or file one online.
The reason why you should file it is that most departments are keeping statistics about crimes that are being used to allocate those limited resources. If their is a spike of vehicle break insin your area, the watch seargent may increase the patrols in that area. The squeeky wheel...
If no one reports anything, then in the eyes of the department, their is no crime and resources can be sent somewhere else (no grease).