You may recall that Eisenhower warned about the so-called "Military Industrial Complex." At the end of WW 2 the GDP devoted to defense spending was just under 40%. It has been falling since then with just a few interruptions. Today defense spending hovers around 4-5% of GDP after climbing a bit after 9/11. If the "MIC" is a "state within a state" it isn't a very successful one given its long slide in the resources it controls which is now only about 10% of what it controlled when Eisenhower was a General of the Army.
Pardon me .... I just made a huge assumption, didn't I? Were you referring to Eisenhower's often overlooked other warning? That one seems to have come true far more than the warning about the so-called "Military Industrial Complex." To quote:
Yet, in holding scientific research and discovery in respect, as we should, we must also be alert to the equal and opposite danger that public policy could itself become the captive of a scientific technological elite.
Man, that raises goose pimples.
As to voting ... Although there are many areas of broad agreement today between the parties*, there are important differences between them too. It's pretty clear that voting for the different parties does mean something. You may recall that Obamacare was a 100% Democratic party vote. If the Democrats in the administration and Congress had been unfettered there would have been another futile "assault weapons" ban, and that didn't happen at the national level although Democrats in various states have pushed something like that through. There are enough differences between the parties and their typical policy preferences so as to make voting meaningful.
* US remains a democratic republic with a more or less capitalist economy, civil rights are good, foreign powers aren't allowed to invade, Europe is a friend, racism is bad, something resembling law and order will be maintained, etc..