MLE, I have often thought that if God can read hearts and needs to clear away the wicked, he could at least do it in a humane way. But, no, there has to be a mean, vengeful destruction. The witnesses actually use the old testament examples, as you mentioned, to solidify this understanding.
Of course, I no longer believe or wish that God will destroy anyone.
I never thought of the materialistic view of the witnesses coming from the fact that they have to give up so much now. It always seemed like most witnesses talk the talk, but do not walk the walk when it comes to not being materialistic. There are those that give up material things to do more, but they are far and few between. In most congos I attended, the elders were often the wealthiest ones. You're right, that is most likely part of the desire.
The witnesses are taught that heaven is unreachable for most of mankind, so they, by default, put all their hopes into living on earth and acquiring large houses and traveling the world. We have a limited time to do these things in our lifespan, so this is very appealing to have endless opportunities in the "new system".
The problem is that the Bible does not teach this. Jesus said to depend on spiritual riches, not material ones. The jws have replaced a spiritual message from the Bible into a material one.