Maybe it's our current pessimistic political climate, but I have a hard time believing that any idealism was involved in the decision for independence; that the founding fathers simply could not abide the violation of their natural rights. It makes much more sense that idealism was used as a cover for what the founding fathers stood to gain economically (reading Howard Zinn certainly didn't help this feeling).
So how much of it was actually righteous indignation at the Crown's actions versus pure, unadulterated self-interest?
This is a bit of a difficult question to answer, as it is always impossible to disprove an overall skepticism towards an idea. Maybe the Founders where just "pretending" and really had selfish goals.
However, I think there are two things that lend evidence towards the non-cynical viewpoint.
The first is what the founders actually said. We don't have to rely on hearsay and general understandings, the founders were incredibly productive writers and wrote a number of pamphlets, books and letters that give us insight into what they were thinking in regards to the Revolution and the proper forms of Government.
John Adams, for example wrote extensively in this regard, as did Jefferson and Madison. These works, generally speaking are echoes of the larger Enlightenment period that is happening in England and on the Continent. I don't think it is fair to say that there is a full scale American Enlightenment, but I would say that there we see the reverberations of these thoughts, the thoughts of Locke, Hobbes, and especially Montesquieu in the writings of the founders.
Adams, again, in his Thoughts on Government describes this, saying among other things (it is quite short, I recommend reading through it) mentions this debt to Enlightenment thinkers, being sure to point out the British ones:
"A man must be indifferent to the sneers of modern Englishmen, to mention in their company the names of Sidney, Harrington, Locke, Milton, Nedham, Neville, Burnet, and Hoadly. No small fortitude is necessary to confess that one has read them. The wretched condition of this country, however, for ten or fifteen years past, has frequently reminded me of their principles and reasonings. They will convince any candid mind, that there is no good government but what is republican." http://oll.libertyfund.org/titles/592
This is something written in the fever of Revolution, but you can see the development of this idea when Adams is a younger man as well, although it has a specifically more Legal idea.
Samuel Adams also echos this in 1772 in a report titled The Rights of the Colonies where is is basically summarizing Locke in his opening statement: "Among the natural rights of the Colonists are these: First, a right to life; Secondly, to liberty; Thirdly, to property; together with the right to support and defend them in the best manner they can. These are evident branches of, rather than deductions from, the duty of self-preservation, commonly called the first law of nature." http://www.constitution.org/bcp/right_col.htm
Jefferson too presents this sentiment. In his Notes on the State of Virginia he discusses at length the constitution of the state and the conditions under which it was developed. It is clear in this proposal that he is establishing the right of Virginia to Self-Rule. (This is a bit more difficult to quote but you can find the full text here: http://www.loc.gov/resource/lhbcb.04902/?sp=124
The second aspect of this is the simple practical fact. Did any of the actually benefit significantly from the Revolution? And the answer, generally speaking, is no. George Washington, not a philosopher or writer of grand sentiments, actually lost quite a bit of money on the Revolution and for the rest of his life lamented this fact. His large land holdings fell into disarray and immediately after the revolution he had to sell parts of his land and take various Tenants to court to force payment of their back rent. Much has been made recently of his "expense account" for the Revolution, but he did incur a large amount of expense serving as the Head of the Colonial Army and this payment was a logn time coming and did not pad his pockets. Washington's continual financial problems are a major theme in Chernov's biography of Washington.
This is also true for Jefferson who was a magnificent spendthrift and died nearly broke. And Adams as well did not profit significantly, he purchased land around his family farm, but he lived there for his entire life and often complained about the expense of being Vice President and President. You can see this is McCulloch's Biography of Adams.