Furthermore, with maxed out storages, it will be easier to and faster to attack and loot villages. You will no longer need to wait for a long time for your troops to cook. The most important thing about these resources is that as you progress from one town hall to another, the cost of searching for villages increase as well. Many times I had to stop searching because my gold storage was running low.
The upgraded Gold Mines should come in handy then. Moreover, war bases are usually made with the town hall and defenses inside and your collectors, mines and other unnecessary buildings scattered around the base. In that case, with your fully upgraded collectors, it will be difficult to break through them and reach the heart of your war base. As a result, they are in fact, essential for war.
Lastly, you should never spend too many gems, especially when training troops. Unless it is absolutely necessary for you to get all those 100 archers trained in a second or you just feel like wasting them, don’t use gems! Instead, boost your barracks and save your gems for a really long upgrade that you need to get rid of.
Stay tuned for more updates on Clash of Clans!