I care more about the relationship end also. Both parties having the mental, emotional, and compassionate stability to endure the tough times as well as the good.
I think, what the signed certificate does is insures each party legal rights over ones assets if something was to happened. This is very important also. If one party gets sick, or God forbid, dies, the stronger of the two has the legal rights to make decisions and/or collect the assets built on the behalf of the other. Without that marriage certificate anyone related or associated (if a business has been obtained) can fail claims over the revenue which was built together by the couple.
So both are equally important. Especially when a healthy strong union has been established and children are involved.