If you're TWF'ing with a Heavy Spiked Shield with two hands and your Armor Spikes as your off-hand attack, do you get the 1.5 STR on your Shield Spike Attacks for wielding it two-handed?
Well, first of all, just to expand a bit, you could only attempt to do this with a heavy shield, heavy spiked shield, or heavy razored shield. In order to make a light shield that you could use with two hands, you would have to increase the size of the weapon, incuring a -2 penalty, but then it would become a one-handed weapon, and thus eligible for a two hand attack. Ironically, this would not improve the AC shield bonus. Weird, but true.
Now the SRD states:
Shield Bash Attacks: You can bash an opponent with a shield, using it as an off-hand weapon. See Table: Weapons for the damage dealt by a shield bash. Used this way, a shield is a martial bludgeoning weapon. For the purpose of penalties on attack rolls, treat a shield as a one-handed weapon. If you use your shield as a weapon, you lose its AC bonus until your next action (usually until the next round). An enhancement bonus on a shield does not improve the effectiveness of a shield bash made with it, but the shield can be made into a magic weapon in its own right.
Clearly the shield must be the off hand weapon. Which means, even if you want to make it your primary attack, it's an off-hand attack, subject to off hand penalties, even if you don't make a primary attack.
Kinda sucks, but that's the way the cookie crumbles.
Can you make a two handed attack with it? Well, at first glance, one might say yes, but we run into the problem that it cannot be used alone. You MUST have a primary attack to go along with your shield.
Now, in your question, you are using armor spikes. I'm afraid the armor spikes must be your primary attack. Can you make your armored spikes your primary? Yes. While it does not say you can under armored spikes, it does say that razored armor is just like spiked armor, and it states specifically that you can use razored armor as a primary, vis a vi, spiked armor can be the primary.
So, you have two hands free to wield your heavy spiked shield. Your shield is a martial, one-handed melee weapon. Any one-handed weapon can be wielded with two hands to do x1.5 damage on str bonus and power attack. So yes, you can do it.
But remember, it's the off hand, which means that if you are making a full attack, the armored spikes can be used multiple times (if you have a high enough BAB), but the shield can only be used as many times in a round as your two-handed weapon fighting feats allow.
In fact, technically, if I was unarmed and had only my shield, by RAW, unless I buy improved two-weapon fighting style, I can only make one attack with my shield per round, even if my BAB is 20.
How to get around that? Simple. Remove the shield from your arm and treat it as an improvised weapon. The DM will undoubtedly have the improvised weapon do just as much damage as it normally does, and it will cause you to take a -4 to hit, but you are free to make as many primary attacks as you wish (and BAB allows.)
I'm going to have to add this one to the weapon handbook.
Oh, BTW, anyone wanna proofread the Poison section? PM me.
