You're the second person to ask that in this thread. Does the existence of their separate entries in the CRB not mean the same thing to you as it does for me?
I see them as two clearly distinct items. Separate, with their own cost, and their own weight.
I can't be wrong on that, right? It's just people not cracking open their Core book and looking for themselves, right?
I see them as separate parts of the same item. Much like the a sword's hilt and a sword's blade. But I can indeed read that section of the core rulebook. Even under the shield spike heading on page 153, it says the 'spiked shield' can be made into a magic weapon, nothing to me implies that you enchant only the spikes independently from the shield.
Irregardless, what I can't do is find professionally published (preferably WotC/Paizo) material with stat blocks with character having +1 flaming (or anything weapon) enchant on their shield spikes particularly when the shield has a separate shield enchantment on it.
What I want is examples to work with. For example, if I wanted to state that the bashing property the the shield spike modification stack (argued at length on these boards), I could back it up by saying look at the Scarred Barbarian (NPC Codex, p. 25). The scarred barbarian NPC, by being a useable Paizo printed example amply demonstrates that the Bashing shield property and spike shield property both do seems to stack becoming a weapon that's base damage is 2d6. (Unfortunately the fact that the stat blocks appears to ignore that shield master eliminates the two-weapon fighting penalties and that it seems to treat the dwarven waraxe as a light weapon discredit this particular stat block a fair bit as well.)
I would be most appreciative if you happen to know where I could find some NPC stat blocks in published material with shield spikes enchanted as weapons I'd like to know where they are located. I do realize that the core rulebook does state that 'shields' and 'spiked shields' can be I would like to see stat blocks where it has been done. I think this will require more effort than just cracking the core rulebook.