The best thing about a marriage (besides the ritual) is the Ring imho. If you marry somebody, who is playing as much as you do, you can use it all the time. Grabbing a treasuremap real quick? Instaport. Going to a Eorzea Icognita place - warp. "Hey, I wanna show you this!" - bling. New quest? Wait a sec, teleporting to you.

Marriage should be aviable through more worlds (as visitor and participant).