Is six in relationship not common? I guess babies in Skyrim come from bottles of mead.
Everything in Skyrim comes from mead. I mean...it's freakin' mead! It belongs at the head of the Nordic pantheon.

On topic, there's more to relationships than just physical intimacy. I think stuff like that should be left to The Sims.
Maybe squeeze in a simple kissing animation at some point, but I agree that video game kissing usually looks really cheesy. However, they could still add more flavor to marriage without "wasting good development time." Give it some gameplay benefits and rewards so that people who don't RP won't see it as "trivial." Spouse-specific quests have already been suggested. Maybe, at some point, your spouse
does go missing or gets kidnapped, and you have to rescue them. Or have them randomly give some simple little quests that have you going to buy food or clothing. Maybe deliver a package to your spouse's friend who lives in another city, and the friend rewards you with gold for the service. Perhaps they want to visit Uncle Bob in Rorikstead and you have to escort them and make sure they arrive safely. When you arrive, Uncle Bob gives you his enchanted spear (Hey, why not? Two birds, one stone). The guilds have generic, radiant quests. Maybe spouses should, too.
I also always have my spouse as a follower on my Dunmer character. Maybe she could have the ability to tend to my wounds after some particularly nasty combat. Sure, I could just as easily heal myself or chug potions, but it would make it feel like your spouse cared for your well-being instead of just functioning like another emotionless follower.
Romance in Skyrim is fairly shallow. I feel that adding things like a-huggin' and a-kissin' without any other substance would just make it even more shallow and gimmicky. It needs more depth than that. Radiant quests, additional special perks, unique dialog that's more diverse, the feeling that your spouse actually cares about you. Right now, we have the Band of Matrimony and Lover's Comfort bonuses. They need more things like that to improve marriage, not just throw in the ability to roll in the hay every once in a while.