I believe the question of gay marriage does meet the concept of justiciability at the federal level and I believe the Supreme Court has made followed those rules to determine the same thing. The Supreme Court can not hear a case unless it meets the terms of justiciability in the first place.
The question of gay marriage meets the concept of justiciability because the cases do not need an advisory opinion, there is an actual controvery between the two parties, the question is not unripe and not moot, and the suit is not seeking judgement on a political question.
The last point is most in doubt, but gay marriage cases ultimately meet it based on the specific criteria that determines what a political question is. According to wikipedia, "political questions include such issues as whether the nation is 'at war' with another country, or whether the U.S. Senate has properly "tried" an impeached federal officer." As marriage is a specific issue involving the rights of individuals in things like taxes and medical care, it does not meet this criteria and thus the issue does meet the concept of justiciability.
The issue of gay marriage in the United States of America is an important issue that must be handled with. The country prides itself with democracy and equality among other things. If we don't deal with this issue we me fall on principal that makes the United States of America a great place.
I do believe the question of gay marriage meets the concept of justiciability because it is a basic human right. This should be a federal right and not left up to the states. Some states are just more bigoted than others, and you shouldn't have your rights denied just because of where you live.