2wd off-road buggies really handle a little better with a bit of weight in them, which is why team guys don't have a problem with running a few aluminum parts here and there.
Milling out the chassis does almost nothing in the way of removing weight, but it does lower the weight that sits in the chassis.
The easiest way to remove weight is to put it on a hardware diet; replace all the stock steel screws with titanium and aluminum.