Well, Improved Weaponry gives +2 damage to all your attacks.
So it should probably cost +1 HP to go from 1d4 to 1d6, not +2 HP.
I could see it being more expensive to get an extra attack, though; a work around involving two-weapon fighting and Heightened accuracy (and maybe a little Super Strength) is a fairly expensive way of getting a second attack.
Morrus,
4CTF is Brilliant! I think it could easily become a system for making monsters, and perhaps even become a class design engine.
I'm really looking forward to further installments.
