Vinegar is likely a bad idea.

Vinegar will attack and possibly damage solder joints, causing a leak
either immediately or long term LIKE WHEN NO ONE IS HOME

Plus the natural corrosion process coats lead solder, so old copper
lines dont leach lead into the water.... thats bad for peoples health
espically kids and pregnant women it can cause retardation.....

thus the big deal over lead remediation.and why lead solder is no long
sold for water line work...

I think its better to find out exactly why flow has dropped, than take
a shot at vinegar which likely wouldnt help anyway and may well cause
troubles long term........

try calling your water company first