It always baffled me that there are no mods out there that develop (or rather, add, in this case) some romance to the game and make marriage something meaningful. And before you say "Oh, but Skyrim is not a BioWare game, we don't need no sappy romance!", consider this: what does it matter to you? Having more options is always better than having less, and really, it would probably not be that hard to improve on the relationship-building in the game, taken that it is pretty much nonexistent now, so anything and everything could be an improvement... -.-
That said, I don't marry my characters in Skyrim because it is just a tacked-on and silly system, and I don't really use companions either, since they get in the way two-thirds of the time (to elaborate: they can be useful if you are a fighter, distracting and getting in the way if you are a mage and completely useless and blowing covers if you are a sneaky thief/assassin/archer; so yeah, two thirds.

).
However, if there was a something, either an expansion like Heartfire or a mod that would flesh out some marriable characters and some post-marriage options/quests, I would go for it. Here's what I was thinking about:
-Wooing:
Add an affection-counter to all marriable NPCs. Also give them a few tags that decide their personality (kind, honest, jealous, etc.). Once they would reach the stage where they would normally be marriable, instead give a new option where the PC can make small-talk with them, and get a random multi-choice conversation. Depending on the answers an their personality, they would either gain or lose affection, and then the small-talk option couldn't be triggered for 24 hours. Once their affection is high enough, marriage finally becomes available, or if it gets REALLY high, they might do the proposing themselves.
-Gifts:
Gifting items to NPC's would also raise their affection-counter, by a degree determined by the item's value and whether they like it or not (women like stuff like gems, jewels and clothes more while men like weapons, armor and tools, though it would also depend on personality). To balance this, only one gift can be given per two days, with diminishing returns.
-New radiant quests:
Simple stuff, like getting rid of another aggressive suitor or doing some small favors for them in exchange of affection and bonuses (money, gifts, etc.).
-Post-marriage:
First and foremost, MAKE SPOUSES USEFUL. With a system like this, wooing an NPC would be much longer and more bothersome, so it requires an appropriate reward, namely: a free perk-point, an always-active buff (depending on the spouse, say, Ysolde would give a buff that grants bonus speechcraft and better prices while Lydia would give bonus to heavy armor and health) and some spousal options with benefits (spending time together -\> would act like waiting but the longer you do it, the bigger temporary stat-boost it gives and for longer, or if you sleep in a bed with them around, you have the option to have sex (offscreen, obviously) which would give a big stat-boost and other benefits). Really, the possibilities are endless!
-Spousal quests:
Funny stuff to make Skyrim more colorful. For example, your spouse complains about not not having any quality meant and sends you out into the wilderness to find a legendary venison. If you do it, you get a full meal with a small permanent stat-boost.
So yeah, if marriage was anything like this in Skyrim, I would love it, too bad it is pretty much a pipe-dream... unless I make it.
