A simple change that can reduce incentives to not buy upgrades
Specifically, I'm referring to the tendency for some people to not buy defensive upgrades because of a perceived advantage in clan wars (regardless of the real impact of such a method on the clan). In most clans, attacking higher than your own rank tends to make people look good to clanmates. That means regardless of it's overall impact for the war, not upgrading defenses tend to make people look good.
To reduce this effect, simply change how your own clan members are listed (and numbered) on the "map". Currently, bases on both sides are ordered by defensive strength of bases. I suggest keeping this display for the opponent's bases, but change the ordering for your own clan to be based on offense rating.
An alternative is to let people select how to sort their "map" in clan war so people who want to know can easily see who really is attacking above their offensive rating.