In many areas you can place two wall traps that will both be in range of each other. If I do this with identical traps, is the damage doubled or would it be better to mix trap types?
Immediate damage is magnified. Extended effects are only accumulated once.
Part of the acid trap's value is in the ongoing damage. This value is wasted if you use two. So traps like fire and acid that do ongoing damage could benefit from being paired with damage only traps such as arrows.