I rode Eroica in Tuscany a couple of years ago. It's simply a fabulous place for riding with lots of small towns with nice eateries, places to sip good inexpensive wine and medieval fortified hilltop castles and villages. As far as dress is concerned and as noted above, european casual is definitely not the same as what many americans consider to be casual (i.e. T-shirts and shorts). You can wear that stuff but you will stick out like a sore thumb (or an american tourist).
The only thing I might add is that your wife might want to have a rental car available if she's not going to ride since it's the countryside and small villages that are so enchanting whereas the trains generally only go to the large cities and towns.