Vows are meaningless? You must have had a bad experience with marriage. Just about taxes? Wow! That is sad if you really think so.
The fact is that marriage is making a comeback and gay marriage has helped. Same sex couples are less likely to divorce, and back when only some states had same sex marriage, opposite sex marriage divorce rates in those states went down also
Gay marriage has made marriage more inclusive and broadened its base. It has more legitimcacy and stabiity as an institution.
The only people who are still whining about gays being able to marry or lamenting the decline of marriage are those who are insecure in their own relationships or have issues with their own sexuality or gender identity. They are threatened by the changes in society that they don't understnd and can't controll. Therefore they have to either lash out at gays and gay marriage, or trivialise and debase the institution of marriage itself