Thanks everyone for the suggestions! It was really helpful.
I had basically got everything down to an idea where using Florence as a base for 4 days. It would probably have been the most fun approach even as speed travelers. Venice and Florence probably was doable, but flirted too close to exhausting vs enjoyable. My wife was pretty receptive of it, but said she wanted to keep tabs on the flight prices to make a decision.
Unfortunately, last night my wife found a deal and made an executive decision to have us to go Lisbon for the 4 days before Barcelona. I mean, for about $2100 round trip for the two of us flights vs $3200-4000 for Milan/Venice flight, I kinda get why she decided to run with the savings and go with the shorter/more direct flight. No Italy.
But yay Portugal.
She did say that when we do Italy next time, she wants to do it right and spend a week and a half and not be as rushed. I'll have a good idea how to proceed when that time comes thanks to your suggestions.