Carrying an extra 500kg?

[OzJavelin]

I'm working on a theoretical project - don't laugh .. SV1/SV2/AP6 Valiant with 3.5L alloy V8 - and was checking out weights of these vehicles (so I can determine if a 215ci V8 can suitably repower a car originally with a 225ci /6). The MAXIMUM weight I can find for one of these is 1218kg. My rough understanding of modern cars is that a Commodore is roughly 1600kg and a Falcon 1700kg ... so modern cars are carrying 400-500kg more weight than their "family sedan" equivalents of 40years ago and they were ALL steel. So despite all the plastic, aluminimum, CAD/CAM, etc we have to lug around the equivalent of 4-5 fat guys just to get down the shops!
Yes I understand all the benefits of modern cars, and yes this is an overly simplistic view, but what about building a smaller, lighter, 6/V8 powered vehicle? Fourty years ago an average family with three kids would fit in an AP6/EH/XP .. why is it now that anyone with (god forbid!) two kids needs a SUV the size of a Hummer!!