I've been considering experimenting with a house rule to say that each success spent on armor penetration gives -2 to the armor die roll, instead of -1.  My gut feeling so far is that -1 is not effective enough to make it worth dropping your wound level, but -2 is significant.

Thoughts?

In the fights we had Wound Level was almost irrelevant.  Once you get 3 wounds on an NPC you're pretty much limited to dink for a wound skip to the next open box.  Once you have the first 3 wounds filled in, you'd need a level 5 wound for it to matter.  So for half of the battle you're not really sacrificing a wound level, because most of the time wounds above the first don't help much.

The -1 is actually pretty effective. It's a statistical effect, so it is easy to overlook it's importance by thinking that on this blow it doesn't seem to make much difference.

It's useful early in the fight as follows. If you inflict a level 3 or 4 wound early on in the fight, you can bet your foe will roll his armour against it with a pretty good chance of stopping it outright. Since the foe is going to roll armour anyway, applying a penalty gives you a slightly better chance of getting through, and your foe may decide: "it's only a 1 point blow, I won't use my armour on it.
The fact is that a 3 point blow early in the fight, and a 1-point blow early in the fight have an identical effect on bringing your foe down. You will still need to inflict 5 more wounds, and the difference between a -1 or -2 penalty on your next action isn't that different.

It's useful late in the fight, once armour is impaired, to make sure you get through that d4 armour, or to significantly increase your chance of getting through d6 armour. I see my players using the -1 in these cases all the time.
Fact is, once your foe has hislevel 1, 2, and 3 wound boxes filled in, there's no reason not to inflict level 1 wounds and use the rest for armour or position bonuses (unless you get a really big hit).

So the -1 armour does have a pretty significant effect.

Thanks for the feedback!