I suppose I will answer my own questions.
It does seem the other purpose of marriage is for the Cause of God to be exalted, such as by allowing marriage between believers and non-believers in the Baha'i revelation. There does not seem to be any other purpose.
I do think with this being a command, it is actually quite important. There is no punishment of course, and this is not something described as being in the realm of the House(s) of Justice, so it appears it is between God and the believer. Throughout Baha'u'llah's writings, He describes how monasticism is a practice which needs not exist, and it seems as though Baha'u'llah really wanted people to be out there interacting and living in the world, for the purpose of remembering God and being an example of God's love and grace.
With Houses of Justice to be in every city, and every city also having a Mashriq'ul-Adhkar, you can envision how community life is supposed to be. A primary purpose which God has for us, after teaching about God, is to create families and communities which embody God's teachings.
So, yes, it is incredibly important to marry and have children, and every effort should be made to create vibrant communities which support family life, from birth to death and every stage between. Will a person be punished for not having children? I do not believe so. I do hope there could be more children who are born being raised under the teachings of Baha'u'llah. In the communities I had served in, it was a rare occurance. I believe because communities are not very focused on developing family life, and much is taught beyond Baha'u'llah which doesn't make family life so attractive in Baha'i communities.
