I don't really care how anyone upgrades. But to be as clear as possible:
For a given amount of gold (and assuming a base with level 8 walls), you'll be able to produce X level 9 walls, or X/4 level 10 walls. Given that the level 9 wall represents the important wallbreaker transition going from two to three wallbreakers required, it's always better to use that amount of gold to produce four times the number of level 9 walls, compared with the amount of level 10 walls you'd be able to upgrade.
Having said all that, I do think level 10 walls look quite a bit cooler than level 9, and I know several people skipping them for that reason alone.






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