The NSRT may not be constitutional, but neither is the income tax and the courts haven't overturned it.
I don't quite understand either of this. Would a sales tax be like an uber-excise tax? And doesn't the 16th Amendment specificaly say income taxes are OK? Now, I disagree with pretty much every aobut an income tax, but how is it not constitutional?
Regarding strict constitutional interpretation, it is interesting to note that most constitutional amendments in recent years have been offered by "conservatives."
In addition to what others have said concerning amendments being the right way to change things, many of these proposed amendments are designed to suplement, not change, the Constitution and make it nearly impossible for the Supreme Court to "interpret" it however they feel.