What I was thinking of was the addition of deeper mechanics for deeper building/mining that allows for the selection of different tools, building materials, and perks to support different playstyles.
For example, we have critical hits, sneak attacks, flurry of blows, headshots, decapitations, stun bonuses, and charging bull hits that all make fighting zombies more interesting. So what if we made it possible to do a critical hits against blocks? At first glance, that might seem a little silly, because all it would do on it's own is randomize the player's damage output a little bit. However, if we add something else into the mix, say, blocks have a higher chance to receive critical hits when they are damaged, suddenly everything gets more complicated and there are a lot more meaningful choices to make when it comes to building. A few fissures in your concrete wall can make the difference on whether a weak zombie can break through with a few lucky hits. You might choose to use a slightly weaker building material because you don't have the perks/tools to repair the stronger building material over 80%. There is more strategy for breaking blocks, heavy weapons/power attacks do more damage, but have a much lower chance to crit, and which one makes sense depends on your active buffs, perks and the durability of the block. A possible strategy might be to weaken a block first with the auger, then smash it with a critical sledgehammer. When you hear the sickening crunch of a critical hit on horde night, you know it means that something that shouldn't have broken has just broken, and that you should be terrified.
I don't think that idea is fleshed out enough for implementation, but it shows that there is a lot more that can be done than just changing some numbers. I don't believe anyone's even touched on the SI system yet in this thread.
