Using lowering coils would, in my mind, improve handling on the roads you describe. In the seventies I always had a Jeep, either a Cherokee or J-10, and always ordered the heavy duty suspension. BUT I would not carry four adult sized passengers in a Sonic, lowered with drop springs or OEM.
As for total weight, I off the top of my head would suggest subtracting at least a hundred pounds from the Gross Vehicle Weight.
On the other hand, if you used coilovers (admittedly more expensive than lowering coils) you could be ok, depending on what coilover makers advises.
I have experienced the results of four adult passengers plus me as the driver in a lowered car: the following day three of the four shocks were bleeding which meant shocks replaced at a cost of $500+ 15 years ago.
Laborsmith