There's a solid reason we don't build cars out of Legos; it's that they aren't solid, as in they tend to fall apart at the mere suggestion of shock. Germany's ADAC apparently got pretty bored recently and decided to test that, so they built a $300 Porsche Lego model then crashed it into a wall.
The Porsche did pretty well, all things considered. Aside from completely falling apart, the car's pieces were mostly intact, meaning that it could be put back together with relative ease.
So there are drawbacks and bonuses. Bonus: Your car isn't completely ruined. You can literally pick up the pieces, sit on the side of the road, and then put everything back together. You know, to drive yourself to a hospital, because you were just in a car crash. Drawbacks: Your car shatters on impact, no matter how slight.
That's some food for thought. In the meantime, enjoy your steel chariots.