The planning stages--maybe 9 months out till day of departure--are thrilling. Once you've bought the air, then you can say 'I'm going!'. That's huge. I can dream every day, and it keeps a smile on my face.
I've honed my planning organizational skills over 3 trips with the help of Excel. Tabs for logistics, tabs for attractions, tabs for restaurants, tabs for packing, all with each day as a structure. What it does is keeps one in check from planning too much, but oddly I fire in on absolute reservations somewhat infrequently. I love having possibilities to do each day, but not be committed to it.
Certainly, for places like St. Peter's or the Uffizi, you make a res. I only travel off or shoulder season, so I have the luxury of day-planning wise, flying kinda by the seat of my pants. Oh, I do buy my Trenitalia tickets way in advance to get as much as a 65% discount on fares. That's worth the risk to me.