We found out our party might be fighting vampires. It could be cool if my shield-bashing fighter affixed wooden shield spikes on heavy steel shield. Can this be a thing, RAW?
The rules, as written, are completely silent on the subject of what materials are used in the construction of shield spikes. If you want a RAW answer, that’s the best you’ll get: the answer is undefined, RAW.
Personally, I always assumed they were metal, but I don’t have any particular problem with allowing them to be wood. Especially if they were some fancy, harder wood, and clearly if you used the ironwood spell there would be zero difficulty, from my perspective. Another GM might require some kind of fancier, harder wood, or even require ironwood.
The other thing that’s unclear to me is if you can add shield spikes to an already-existing shield. The rules don’t say; I kind of always assumed that a shield and a spiked shield were two separate items and you couldn’t convert from one to the other, but again, that’s not written anywhere. I guess the fact that shield spikes are in the “Extras” section might imply they could be added on later? Anyway, I certainly wouldn’t block a player from doing so if they wanted. But again, that’s not RAW; RAW is just silent.
As this other answer already explains, there is no rules as written for wooden spikes, so you will have to GM Fiat a solution there.
But I would like to point out that a Wooden Stake is a specific item in the game, and simply using pointy-wooden-weapons might not be of any help against vampires.
Vampire Weaknesses says:
Driving a wooden stake through a helpless vampire’s heart instantly slays it (this is a full-round action). However, it returns to life if the stake is removed, unless the head is also severed and anointed with holy water.
There is no mention of other commonly made of wood weapons, such as javelins, arrows or even spears. That said, I believe the weakness to wooden stakes is rooted in mysticism, and not an actual weakness against having their heart pierced by wood. So your GM would have to specifically allow that exception to work. Personally, I know I wouldn't let it work, but you sure are welcome to try and I would never try to stop you.