A 520e (final clarification to Q 520a)Yes. The armor spikes weapon has its own attack bonus, its own weapon enhancements, and its own penalties for nonproficiency "when you try to use them". You would be ignoring all of those RAW elements if the damage is automatically "extra" when using some other attack in a grapple. You must "try to use them" and succeed, as specified in the item description, to add that extra piercing damage.
A 520f (final clarification to Q 520b)
Already answered.