If the USA were suddenly poor, would the people be more religious or spiritual?

Religion has more to do with illiteracy then poverty. So being poor is not the reason to turn religious.

That is impossible to answer, since human reactiions are varied. And you have to take note that it is now not only the various sects of Christianity which are involved - there are many Buddhists and Hindus and Muslims in America, not to mention the various hippie cults etc which might claim a 'religious' basis. And what about the Native Americans? Apologies for leaving them to last.

Why do people take shelter with the religions? Because they want to get rid of earthly cares and be happy. So, certainly the Americans will become spiritual when they will realize that this world is an empirical one and there no reality in the material world. Now they are ignorant and that is why they are capitalist and try to rule upon all.

Depends. The human mind is a very complex system, so one person might go all religious and another person might become an atheist, etc.