Although I love pretty shoes when I'm not going to be walking around a lot, when I have a lot of errands to run or when I travel I throw foot fashion out the window. (Not the rest of my outfit, though ) I know I'm in the minority but I LOVE my plain black Skechers Shape-Ups, even though they don't actually do the butt-tightening etc that the ads claim. These shoes are as ugly as the day is long, but they are like walking on pillows, and I don't want to be in pain just so people I don't know and will never see again, and who couldn't care less about me, might look at me as I hobble by and think "cute shoes."
Having said that, those Josef Seibel shoes are wondrous and I hope you get them. They would go with everything and look adorable doing it. I just think a back-up pair is well worth it, even though I'm on Team Pack Light too. Three weeks in a single pair of shoes is a lot to ask of your feet and they will appreciate the variety (especially on rainy days when you don't want to risk ruining such adorable shoes).
My parents just went to Rome and walked for hours a day and were actually in a fair amount of pain because of all the miles they logged on cobblestones--all that uneven distribution of weight on every step--so if you're going to be walking a lot in the old parts of cities, I would urge you to consider a pair of shoes with a really thick sole. Like, oh, I don't know, Skechers?