What is the point of upgrading your stash? Well now that we have run the numbers (see the table below) we can see that in order to get to Level 30 it will cost:

300420 units of Wood
382765 units of Clay
212905 units of Iron
85090 units of Food

All this in order to be able to protect the grand sums of 16000 should a Cowboy or Mexican player raid/attack and 5344 should an Indian player raid/attack. Meanwhile you'll be burning through 45 units of food per hour to keep this awesome ability to protect 16000/5344 resources.

So the question must be asked...is it even worth it?

Cowboy - The amount of resources safe per level from Cowboys and Mexicans.

(Cowboy) - The amount of resources safe per level from Indians.

Mexican/Indian - The amount of recources safe per level from Cowboys and Mexicans.

(Mexican/Indian) - The amount of resources safe per level from Indians.