I understand your reasoning but in my experience an enemy with 80% lvl 9 walls is scarier than a base with 30 lvl 9 and 10% lvl 10. Also when I see someone wth 3 different levels of walls (regardless of walls levels) I see them as less experienced players so in short I think your idea would have a lower fear factor.
Why would fear factor be more important than efficinecy and effectiveness in protecting your loot? Besides once you get 50 lavas even with some skulls trust me people get afraid. I never get attacked anymore really.