I thought you only get crits when you roll an attack. You don't roll an attack with a spell stored sword/weapon as far as the spell is concerned. It is use activated/free action. If you had to roll a seperate attack for the spell then I would allow it. You are basically autohitting with the spell even if it is conditional on the sword hitting. I treat it as extra dice of damage just like sneak attack or elemental (flaming etc...) damage dice.
Just another way to look at it.
later
Just another way to look at it.
later
