Wouldn't heavier launchers be cheaper in terms of fuel though? FH can lift five times what F9 can, and uses, what, three times more fuel? If you:
1. Developed full reusability all the way to Mars.
2. Increased the size of the rocket/engines.
True as that is, the cost of the fuel is a VERY small expense for the overall launch budget. Off the top of my head, the larger and more sophisticated engines alone would easily offset any cost savings in fuel efficiency, to say nothing of the added cost of the rocket itself, extra man hours needed to get it flight ready, and the fixed cost of the larger and more complicated launch facilities needed to maintain it.