Alea-something to consider re-your question.
The US Constitution is not amended very often, that's true. But there is a way in which the document is fairly adaptable. First, the Necessary and Proper clause allows for some flexibility, as do the provisions that the federal government has the right to control interstate commerce. Second, the power of Judicial Review (which isn't really in the Constitution, but for which we can thank -or blame- John Marshall) allows the Supreme court to review new issues and, in essence create additions/modifications to the Constitution.
Over the years, this has allowed the court to rule on issues which developed after the founders wrote the initial document, like creating the Bank of the United States, requiring educational integration, and regulating the Internet.
This power has been used for great evil, like the Dred Scott Decision, which invalidated the rights of every African American in the US, and for great good like ending slavery and the Brown v Board of Education decision.
Like any law, the constitution is only as valuable and just as the people enforcing it. It is here that the failures have been, more than any shortcoming of the document, itself.
The greatest danger IMO, is that we will allow a situation to develop in which one party takes a super majority on the court, creating an unacceptable bias in it's decisions. We might also eventually get another President who tries what Andrew Jackson did in ignoring the Worcester v Georgia decision in allowing the beginnings of the removal of the Five Civilized Tribes. As someone who is part Cherokee, that one affected my family directly.
AI
