Well, part of the cleverness built into the constitution is a meta-rule describing the process for changing the constitution. Every system accumulates cruft, but if we have a mechanism to apply patches, then we can (in theory) accomplish some refactoring without an upheaval.
The only issue is that modern politics in America is a lot more like trench warfare, with lines drawn and and fixed. Opinions on every issue fall along party lines, with a few exceptions.
I hope dearly that Lawrence Lessig succeeds in actually calling a constitutional convention (http://www.callaconvention.org), if for no other reason than to strike out your "in theory" qualifier.
The only issue is that modern politics in America is a lot more like trench warfare, with lines drawn and and fixed. Opinions on every issue fall along party lines, with a few exceptions.