The question regarding Counterspell is not whether or not the person casting the counterspell has to figure in Impedance (he does), but if the target spell/caster has armor, how does HIS Impedance figure into the calculations.
For example:
Fred the Black Magican is wearing Scale torso armor and is casting Hex (4 SP), thus he is spending 6 SP in total to cast the spell (and if we use Witchking's suggestion and use double the Imp as a CTN mod, the Casting TN of the Hex is increased from 26 to 30).
Joe, our magical hero is going to cast Counterspell (Joe is NOT wearing armor right now). He makes his Magecraft roll so he knows how many SP he needs to counter the Hex.
The question is -- When Joe makes his Magecraft roll, does it tell him that the spell costs 4 SP (its normal cost), or 6 SP since that is what Fred spent?
Personally, I would say 4 SP, since it seems wrong to me to force a Counterspeller to also pay for the target's impedance. It would also mean that something that makes a spell harder to cast also makes it harder to dispell (counter-intuitive to me).
Saves -- I was talking the target's Saves... If Fred is casting Hex on Joe, Joe's Save TN should be (IMO) 18, not 20. Now, I could see an argument for making the target's Save be 16 (14 + Base SP in spell - Imp) as THAT does make sense to me.