This game has answered the question "What happens when you tie four ramjets onto a pickaxe with a shuriken attached, and throw it at a man who is swimming?"
I think that the tunnels you make should stay for longer, and if you use them you should get a speed boost. The most used tunnels should stay for ages, and maybe the stick people will dig down and create barricades, plant land mines etc.? Or maybe even you find some Chilean miners!