Does each state have a strong collective identity, or is it rarely expressed?
Yes, and yes. Americans seem to be oblivious to the fact that Americans in different parts of the empire are very different from one another. Yet the entire history of the US is ethnic strife between regions. Take the Civil War for example. The North says that it was about slavery, the South says that it was about states' rights. Both views true but superficial. The truth is that New Englanders and Southerners don't get along and both sides wanted to expand their way of life into the western territories.
Due to our two party system, the various ethnicities have to form coalitions. So right now New England and the Pacific regions are with the Democrats, and the Interior West and the South are with the Democrats. The Midwest is the swing region. These coalitions hide many of the regional differences. For example the Republicans of Georgia and Wyoming have very little in common.
Because Americans do not acknowledge the fact that American politics are driven by ethnicity people use proxies to distinguish friend from foe.
Modern US politics is dominated by really trivial issues, that we call "wedge issues". The US is in a very secure situation. The idea of a military invasion is inconceivable and so US foreign policy can be capricious rather than focused on strategic concerns. So things of no importance to the US drive the foreign policy, such as the latest in Israeli settlement activity or gay rights in Russia. These things cannot possibly affect Americans, and yet they receive a huge amount of attention.
Other issues are just as trivial. The more passionate people are about an issue the more likely it is to be a wedge issue. It is really just like people's loyalties to sports teams, entirely silly.
But remember that this is all under the surface. Many people just look at themselves and their neighbors and say "we are Americans". They have no real awareness that by defining themselves as "Americans" only they are therefore defining the term in such a way that it doesn't fit other Americans, which is what causes the petty struggles that dominate US politics.
For example, is there any obvious disquiet about the disproportionate contribution to the economic situation that somes states seem to have contributed?
Yes. Many resent the fact that all of our money goes to DC, NYC, their surroundings (Maryland, Connecticut, New Jersey) and a few other places favored by the elite. Sometimes you will see an absurd map floating around claiming the opposite, these maps show DC, Maryland, and NYC being the ones supporting the rest of the country. Ha. DC's only export is government. NYC's main export is banking (meaning that they are pulling money from the rest of the country). Maryland is just where DC workers live. For example we live in Maryland because my wife works in DC. She works in DC because DC prints the money. We would rather live somewhere else, but other places don't have the ability to print infinite money. If bitcoin ever replaces the dollar we will see a total collapse of DC, NYC, and a few other places.