A/ The mathematical chances are high, that another captain will attack you, thus depending on the tournament you are in, at that time, you can calculate the mathematical appropriate defence, to give you maximum points in that tournament.
This means in theory you are calculating or swapping resources for points, calculating what you lose you get back more in the tournament.
If no one attacks you,( highly unlikely ) you simply gain the treasure and use it as you see fit.
B/ I would change some of the islands to give 2 treasures simultaneously say Lumber and say Rubies, making it a more attractive place to hold a larger defence, thus making it more of a reason to 1 attack it and 2 defend it.
Factoring in a system where by you can only go to the treasure at certain levels, a level 5 island cannot be attacked, defended, farmed by any level over 5, would open various different little competitions for that level of island.
The code changes would have a significant time period to implement, I would suggest some sort of grading, say 5 to 10, 10 to 20 20 to 30 etc etc, this way a higher level could not easyerly knock a set of Treasure at level lower than his field of allowance, in layman’s terms the big boys fight the big boys, and the small boys fight the small boys, compare it to say “Boxing”
This gives smaller levels an incentive to win there " weight / level " thus in theory making more money for the game via that ambitious player possible investing their money, safe in the knowledge, that there not going to get bullied and it will not be a waist of time.