When I talked about the bash, hack, jab, and stab attacks and offered the slash attack as a variant, I also had another variant in the back of my head: adding spikes to a bash attack. After all, if a rod modified to give it an edge changes the behavior of the attack from bash to hack, adding spikes to a club should have some effect as well.
The first obvious conclusion: adding spikes adds the opportunity for bleeding wounds, the same as adding an edge or point would. So, roll to see if bleeding stops at the end of every day or take an additional 1d6 damage.
The problem this raises: what's the difference between spikes and stabbing with a spiked pole (spear, etc.?) Stabbing, as a variant of jabbing, focuses more of the weight of the weapon behind the narrow point, making damage the best of two 1d6 rolls. Does the same thing happen with short, spiked clubs or spiked balls?
We could go that way, or we can instead treat them as similar to edged weapons, but with an ability to impale instead of sever limbs.
This raises another question about weapons designed for more than one kind of attack (spiked mace with prominent point on the end.) But I think I will need to cover that later.