Yes, as you have easy contact with a lot of people in the immediate neighborhood, I would certainly ask around your own cul-de-sac and the adjoining/opposite ones, as you're likey to be fed from the same transformer. If several other neighbors have been experiencing similar problems, it's most likely a problem on the network (cable splice going bad or something similar) and a call to the local supplier would be in order to report it.
As the dips are affecting all the circuits in your house, if the fault is on your own equipment it will be on that part which is common to the entire installation. That pretty much narrows it down to somewhere between the meter and your main distribution board. It's fairly easy to check for loose connections etc. in the latter, but I would be reticent to suggest doing it yourself as some points inside that box are still energized even when the main switch is turned off. A local electrician should be able to check it for you, and put a meter on and test under load to see if there appears to be a problem on the incoming supply.
Everything from the cable which runs from the street, through the main fuse cut-out, up to and including the meter belongs to the supply company, so if your own equipment appears to be all right and you are still having problems, I'd suggest calling your supplier and get them to check out their equipment.