I think maybe the biggest unintended consequence of this war was the impact that it had on the United States economy. Before the war, they had been a part of the richest empire on earth. After the war, they were a tiny country with a relatively weak economy. The recession after the war was surely an unintended consequence of the war.
The other big one that I see is that democracy was an unintended consequence on the part of the elites who started the rebellion. They did not anticipate building a country that was as democratic as what they ended up with. That's a trend that they tried to stop with the Constitution, but that only delayed it a bit.
The most unintended consequence of wars is that in almost every war one of the two parties to the conflict loose it, though in most of the cases both the parties expect to win it. Thus on average about half the times people engaging in the war loose it, which is very much an unintended consequence of wars.
Also, usually wars cause much destruction and distress for both the parties in the war. These consequences are not intended but these are most certainly expected. What could be unexpected is the extent of losses incurred. Usually people do tend to underestimate such losses.
In American war of revolution also the hardships expected by the people at the beginning of the war must have been quite low as compared to the final outcomes. Unless this was so it is quite unlikely that general population would have supported the war. However, as the war progressed, the expectation of hardships and along with that the determination to continue the war must have increased.
In the end the American people won the war and laid the foundation of a big, prosperous and powerful nation. The basic victory in the war was definitely the intended consequences of the war. I am not sure if the extent of size, prosperity and power that USA has now gained in relation to other countries of the world was expected at the time of American Revolution.