I always get upgraded when I go to the WL...and I am pleasantly surprised each time!
If I were you, when I check in, just be in an upbeat, bubbly mood. they usually ask you how are you, etc. Tell then how happy you are to be celebrating your anniversary, you've been looking forward to this trip, etc. Ask the CM "for your most romantic" location...that is not asking for an upgrade, but I bet if they have one, they will give it to you.
Hope you have a great trip...DH and I just got back from WDW where we celebrated our 8 year anniversary. This was our first trip without DD(she is 6) so it was kinda cool!