Two Weapons + Spike Shield?

[MikMod]

ITL p41: "Any character can fight with two weapons, if one is .. a spike shield"

ITL p41: you can "make an attack with one weapon, and parry with the other, which acts as a shield to stop 2 points of damage..."

So if I equip myself with a spike shield, I can use 2 weapons talent to turn it into a 2 point shield? Or is that a 3 point shield? Since I assume it still protects for 1 point if I 'use' it for a second attack, so why would I lose that point if I parry? And why on earth is the spike shield the only shield I can use like this?

Subsidiary point: Can any character simply use a left handed dagger as a '2 point shield' in every fight without needing shield skill or to lose a point of AdjDX?

I feel I must have missed something (again)