To What Extent Is Marriage (Gay Or Not) A Matter of Constitutional Law?

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Much has been said about this subject over the past few days, and I will admit that I have had trouble getting my arms around the issue.  I think almost all conservatives would agree with me that marriage between a man and a woman is an ideal that our society should promote, and that gay marriage would undermine and weaken that institutional ideal.  That's why Proposition 22 passed in 2000 in California.  It essentially states that only a marriage between one man and one woman is valid or recognized in California.  I supported Porp 22 in every way possible and voted for it.
 
The problem we all have is that other states may not take that approach.   In Massachusetts, for example, the state supreme court has found a right to gay marriage in that state's constitution.  Thus the "full faith and credit" clause of the U.S. Constitution give us our legal issue:
 
"Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State." 
 
Under this clause, a contract entered into in Nevada is enforceable in New Jersey.  Marriage is a contract, so a marriage valid in Massachusetts must be valid in California, and the U.S. Constitution would override California's Proposition 22. 
 
Now, the Constitution also gives the Congress power to "regulate" the way in which contracts are enforced from state to state under the full faith and credit clause, but there has been little judicial review of that provision and many scholars do not believe the U.S. Supreme Court would uphold California's Prop 22 against a challenge from someone with a legal gay marriage in another state.  It's more complicated than all that, but that's the basic idea.
 
So for me the problem has always been that I hate to see the Constitution amended unless that is the only way to achieve an important goal.  It seems to me that nothing short of a Constitutional amendment would suffice to resolve the marriage issue, because having marriages valid in one state but invalid in another would be such a mess. 
 
Then I saw these thoughts from the always excellent Power Line.  Read them.  The author concludes that marriage should be left to the states, and that the "full faith and credit" problem should be solved by amending that clause as follows:
 
"Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State, EXCEPT NO STATE SHALL BE REQUIRED TO GIVE FULL FAITH AND CREDIT TO ANY MARRIAGE ESTABLISHED UNDER THE LAWS OF ANOTHER STATE."
 
I must admit, it's an intriguing approach, but I still wonder:  We'd end up with a patchwork system in which people might be married in Arizona and not married in Utah.  There could be chaos over property and inheritance rights, and divorce lawyers would have a field day.   But at least the people of each state could decided fundamental cultural and life questions for themselves-- just the way they should be able to decide abortion rights, if it were not for Roe v. Wade.