I'm gonna give a little history lesson here to set up my thoughts, but I do understand this is common knowledge so please don't think I'm being condescending by telling you something you may already know.
America was founded on the will of the people (that's where the phrase "of the people, by the people, for the people" comes from). The people sent their representatives to embody their will into a legal document to govern them, and the first such attempt was the Articles of Confederation. But the AoC sucked because it treated the United States as literally that - united, yet independent states (as in countries), which retained their powers over the uniting government. Predictably, this ended in disaster, the most noted of which was the creation of a seperate and distinct currency for each state, but also in large part due to the fact that larger states had to pitch in more than their fair share of the work (based on population) because they only got one vote (each state was allowed only one). This led to the creation of two houses of Congress under the Constitution, one with vote weight based on population and one based on equality of vote.
The second attempt, the Constitution, went much better because it created the "America" part of the United States - one country which we all live in, one law which we all live under (and thank god one currency which we all use). The reason we stick to it so devoutly is because to not do so would invite things and people which would not only destroy our unity but defy the will of the people and go against everything we stand for, everything we are, everything the Revolutionary soldiers (and all those that came after too) died for, and the very reason America was created in the first place.
The Constitution was designed to set up the government of the Union and the individual States, whilst the amendments (and Bill of Rights) were designed to allow for specific rulings and guidance on specific issues as they arose. The Bill of Rights is not specifically the most important of all rights, just the ones the Founding Fathers decided were important enough to spell out at the time. I would argue that the right to bear arms and the limit of two presidential terms serve the same purpose (to prevent tyrrany) and are therefore equally important, despite being ratified about a century and a half apart.
The reason the Bill of Rights is (or at least should be, and is by me) seen as the most important is because those rights apply the most directly to preventing tyrrany. I'm just sad that 11, 13-15, 19, 22-26 took as long as they did to be included, let alone had to be spelled out seperately at all (to be fair, some of those circumstances could not have been easily foreseen, and in the case of age and term limits some argument as to the *exact* limits was needed). I'm also saddened that we wasted two on alcohol, yet have done nothing about drugs.
The concept of Unconstitutionality takes into effect the entire Constitution, amendments and all. The Constitution is a living document and therefore *can* and *should* be changed when it is for the betterment of or at the will of the people. From what I understand, the purpose for amendments was to add to the Constituion guidance and rules for specific situations as they were encountered, not to take away from or negate any of what was already written. The power of negation was a good thing when it came to Prohibition, but I would not want to live in an America where any of the other amendments or parts of the Constitution were repealed. All it would take is electing the right idiots and they would vote us out of every right we have. That, and not nationalism or tradition is why the Constitution is so important and is seen as the unquestionable law of our land. Those are the pros and cons of sticking to the Constitution, though I don't think age matters on rights as important as suffrage. Suffrage is good regardless of age.
Another thing I feel worth mentioning is that most debates on Constitutionality (or the lack thereof) have revolved around the Bill of Rights. I can't rightly explain whether or not there is or should be a specific reason for that, but there you go. Perplexingly, I understand that Constitutionality is an argument to determine the spirit but not the letter of the law, as the amendments themselves *make* the letter of the law. Constitutionality is an argument to keep our laws in a concurrent spirit, and to determine that our laws do not harmor unfairly restrict the will of the people, not an argument of violation of actual established principle.
As for infallibility, I feel that there should be a process to determine the permanency of some laws. I doubt anyone would argue against the permanency of the abolition of slavery, or the right of universal suffrage. We need such laws to be protected from future attempts of tyrrany. But I would not want to see automatic permanency for all laws (I do so love my Samuel Adams beers!).
Despite a system of checks and balances designed to keep that very scary situation from happening, all it takes is the aligning of all three branches in conspiracy and the law will be rendered moot. I feel that this makes amendment 2 (and the US currently having 9 guns for every 10 people) our "fourth check and balance," which is why so many people make such a fuss over it.

In all seriousness, the threat of foreign invasion is just as important and likely a reason to form a militia as the rise of tyrrany at home. I would, however, like to think that the will of the people is stronger than the corruption of elected officials, and those who implement the law will not let those who write the law get away with shennaniganery. In other words, open and nationally united defiance is better than guns.
I like what Cheeze_Pavillion said about sovereignty in post 31. So instead of repeating it here, I advise you to read it if you have not.
And last but not least, for the fella that thought Congress couldn't just abolish Presidential term limits, well, read the damn news. Jose Serrano (a Democrat, don't get me started) wants to do just that so Obama can be President for life. And he isn't the first to suggest such a measure, but with Obama being President it's the first time such a measure is being taken seriously. The Constitution is called a living document because traitors like Serrano can easily kill it. And then those who dissent, like us.
While there are arguements on the specifics of fallibility and enumeration, I think we can all pretty much agree that dicking around with the Constitution dicks around with our rights and subsequently how we are or are not allowed to live. It should only be done in the most serious and grave of situations.