Spiff - Thanks for posting that list. I was hoping you would do so. I knew that there were many areas of government where marrital was a consideration, but I wasn't able to draw examples outside of taxation, etc.
Craig - Again, I do understand your position about wanting to revamp government rather than expand it. Trust me, being a Libertarian, I am definitely for smaller government. When it comes to those individual reforms, I got your back should you decide to march.
However, the root problem here is that the changes you recommend are massive and will take a significant amount of time to implement, if ever. During that time, you still have a glaring inequality in how the government treats and benefits one group of citizens over another.
Finally, if you take a look through that massive list that Spiff posted, you begin to see that the protection afforded to "Spouses" and "married" persons in the eyes of the law expand far beyond the reforms you are suggesting....domestic violence, divorce, allimony, bankruptcy, veteran benefits, inheritance, student loans (responsibility), political candidacy, welfare, social security, child support/"Deadbeat" laws, etc, etc... Therefore, even if you assume that all of the reforms you mention are implemented, government consideration of marital status will still be present and prevalent.
In the end, no matter how much you want to make marriage a religious institution, it's not in the eyes of the government. It's a classification that carries massive amounts of benefits, protections, and responsibilities that should not be denied to a segement of society because it goes against popular opinion and/or religious sentiment.
For the record, "civil unions" works for me, as long as the laws treat them the same as marriages. After all, I am only advocating for the change of laws here. The religious ramifications are for the churches to deal with, fight over, and hopefully eventually come to terms with.