On this subject, while I totally agree with you that spikes aren't useless, don't you think that a base with 4 rows of spikes (to start, might get to 10!) looks a bit silly?
I think you could achieve the same balance by making each individual spike costlier (in materials and in time) than they are now, but also more durable. That way, you spend the same materials for a single row of spikes than you do now for four of them, but they are just as effective as the four rows and you don't have a base that ends up looking like a huge sea of spikes.
This would also discourage crafting spikes on the fly as a means to kill pursuing zombies, since each spike would cost more materials and take more time to make.