Upgraded 3 lvl11 walls and 4 lvl12 walls today (21mil total resources)
3 days between upgrades mean that I only farm 2 out the 3 days and resources just overflow in the last day. This is why I always recommend 1-2 day gaps between builders so because 3 days will let almost anyone overflow. Overflow is bad because the loot cannot be spent on walls. If you really farm a lot and unable to keep 1 day gaps, consider having an idle builder just for walls. This allows you to continue farming all the time.
Upgrading a spring trap right now so that I can have a builder in 2 days time, not really expecting it to help much. The only reason SC buffed spring traps to have levels in the past is just to nerf valks, beyond lvl2 there is no real reason to upgrade spring traps at all.