The Constitution cannot be changed whenever you want because the amendments need to hold up to standards years from now and not just what's popular today because a few people pushed it -- remember Prohibition?
As for the natural born rule, I think it should be in place. what happens when Arnold becomes president and favors Austria over other countries for trade agreements, economic aid, immigration, etc.? Whether he does it on purpose or not, there will always be suspicious by the international community. And yes, if this does go through, as Irvine said, Jennifer Graholm would give Arnold a run for his money. Not to mention there is no way the majority of America would vote for him -- when it comes down to it, those "moral value" red states will have problems with his stance on abortion, stem-cell research and gay marriage and would never vote for a guy whose claim to fame is violent movies.
He should just give up and be happy he has California.