It does in my experience. When I'm not at work I prefer to be barefoot. I've accidentally stepped on nails while walking and got pricked. Then once I was running and it went all the way through.Hitting harder a needle doesn't mean you will deal more damage to your self.
If you hit it slowly then you'd pull your hand away instead of letting it slowly sink in. If you just hit it less hard you can't drive it in as far, thus dealing less damage.You are thinking "pierce you skin with the quills, but still hit the porcupine". So, if you have a +10 strength you will hit it harder. If you have a -5 strength you hit it softly. In both cases you have pierced your skin with the same needles. The -5 might actually mean you did it slower and it was more painful. Practically, hitting it harder is your best choice because of that.
You still damage the porcupine if you get past its armor class, you just hurt yourself while doing so. There are a number of other creatures that do this as well.
Even with thick gloves I've punctured myself while grabbing hold of blackberry vines. Porcupines have quills nearly a foot long. There are also other published creatures that cannot do damage to creatures with a certain AC. That's what gave me the idea.Also, if you are wearing a full-plate or simply some gloves, your attack is still unarmed, but practically you wouldn't be dealt damage at all. So the +5 natural armor "shield" doesn't make that much sense. Don't go into that much details, because you would also have to think WHERE the natural armor is (maybe it is not on your palms that you are using to hit it with).
That'd be kind of funny actually. I think I'll add a cap, up to +5 strength bonus.Furthermore, mechanic-wise spikes don't work that way. Because you don't want the super-strong-leveled-up Barbarian punching a porcupine and being dealt 1d4+40 damage. And the super-weak-noob Wizard punching it and being deal 1d4 damage. Makes no sense.
There is a big difference between punching a surface and being stuck with a needle. See my foot reference above. I can run on gravel and break bricks with these clunkers. A little nail or thorn can still puncture me good and proper.You also don't want this Master Monk that can pass a Golem's iron skin without feeling pain with simply a high Basic Attack (high skill) being dealt a lot of damage from some porcupine's needles.
Except porcupines can be petted while happy. They only stick up their quills when threatened.I have to add also that you might want to add the occasion of stepping on it, to have it like a trap in a dark room. You won't be attacking or grappling with it, so you won't be dealt damage. You should add this as well.
Though I appreciate your time and effort, I can't agree that the changes make any more sense, and veer into way too much effort for a simple mechanic.