Happy Anniversary to you two! I have to agree with sounds_sound. gq and I tend to stumble through our trips. If we are in a new place, we typically pick a few things to be seen, or places to go, but we leave the 'when' and 'how' to the moment, and reserve the majority of time for whatever strikes us. Most of my best travel moments don't directly relate to the place I was, but something that happened to me while I was there.
M and I like to have a short list of places we're keen to check out when we're in a city. No nailing them down to a particular day, and no committing to all of them. Just a list of places to head to if we don't have anything better going on. A lot of the time we just end up exploring new territory. Sometimes the list I mentioned is secret and M doesn't even know about it, -I just note a couple places I'd like to take her that I think she'd dig if the day permits. Sometimes the best plans are secret plans because nobody except me knows (and therefore cares) when they get broken :p
Every year on their anniversary, my parents get in their car and essentially flip a coin as to which direction they will go. They drive until they reach a place they've not been before and that seems appealing to them. From their accounts, it seems to be a fantastic way to travel. IMO, expectation is an executioner of sponteneity. Best to leave them out of your plans.