marriage and peru u'revu: two mitzvos or one?

One of my kids asked me whether the "purpose" of the mitzvah of marriage is so that one can fulfill peru u'revu, or whether it is for the sake of the relationship.

I want to preface the sources below with two comments: 1) I don't like questions about the "purpose" of mitzvos.  Contemplating taamei ha'mitzvos seems to me to be a purely speculative exercise; what G-d's "purpose" is is probably beyond what any of us can fathom.  That being said, as the Rambam writes at the end of Hil Temunah, "Af al pi she she'kol chukei haTorah gezeiros heim... ra'uy l'hisbonen ba'hem."  I would rephrase any question of this type into a question as to what lessons we can derive from the mitzvah to enrich our appreciation of it.  2)The idea that marriage is only for the sake of peru u'revu came from some teacher (granted the possibility that the message was misunderstood).  However you interpret the sources, for all practical purposes I shudder at the thought of a marriage built around that purpose alone.  From a chinuch perspective, I think that is not the message anyone should be giving.  

My initial thoughts based on some sources:

1) As R' Soloveitchik pointed out in Lonely Man of Faith, there is dichotomy between what he called Adam I, the story of creation in Braishis ch 1, and Adam II, the story in Braishis ch 2.  Without going into all the differences between the stories and what it tells us about man's mission in the world, the dichotomy also expresses itself with respect to the creation of woman.  In ch 1, the Torah just tells us that man was created zachar and nekeiva and Hashem gave them a blessing and said peru u'revu.  In ch 2 we have the idea of eizer k'negdo, of woman being a helpmate, not just a partner in fulfilling periya v'rivya.  So already from creation, we see both of these elements at work.  

2) The Tur opens Even ha'Ezer:

יתברך שמו של הקב"ה שהוא חפץ בטוב בריותיו שידע שאין טוב לאדם להיות לבדו ועל כן עשה לו עזר כנגדו ועוד כי כוונת הבריאה באדם כדי לפרות ולרבות וזה אי אפשר בלא העזר ועל כן צוהו לדבק בעזר שעשה לו לכך חייב כל אדם לישא אשה כדי לפרות ולרבות

Here too we see two reasons for marriage: A) eizer k'negdo, to have a helpmate; B) to procreate.  These are not necessarily mutually exclusive.

3) As we once discussed, the Rambam and Rosh (Kesubos I:12) debate whether birchas eirusin is a birchas ha'mitzvah because there is an independent mitzvah to get married, or whether it is a birchas ha'shevach because there is no mitzvah per se to be married, only a mitzvah to have children.  If one assumes kiddushin in an independent mitzvah, it suggests that it has value even beyond peru u'revu.

4) There is a din (Eh"E 1:8) that even if one has fulfilled peru u'revu, one still has an obligation to be married.  At first glance this seems to indicate that there is an importance to marriage even outside the context of having children.  However, in truth this din 1) may be an eitzah tovah and not even a real takanah; 2) may simply be for the sake of avoiding hirhur.  On the other hand, Pitchei Teshuvah quotes a RI"F that suggests it may be a din d'oraysa.

5) In the new editions of the Minchas Chinuch in footnote #18 to the mitzvah of peru u'revu they quote that the M"C's son-in-law said that when the M'C was mesader kiddushin he would tell the chassan, since mitzvos tzerichos kavanah, to have in mind that his kinyan ishus was for the sake of being m'keyeim the mitzvah of peru u'revu.  Clearly he held that you cannot seperate the two kiyumim.  Anyone know of anyone out there who does this?