In how many days do you plan to make the trip from Spoleto to Florence?
Option 1 is probably the more logical choice if your last intended destination is Florence.
Regarding your option 2, if you care to take that route, I wouldn’t care to make the trip all the way to San Marino. That’s too far and a major detour on the way to Florence.
However along that route there are very historical places of interest, which are closer by, such as Spello, Assisi, Gubbio, Anghiari, Arezzo.
North of Arezzo, the Casentino valley has Poppi, Camaldoli, and La Verna (St. Francis), among others, in addition to the National Park of the Casentinesi Forests, the largest forest park in mainland Italy with 368sq.km (the largest in Italy is in the island of Sardinia).
The issue is time, however. If you plan to make the trip on a day, you have time for just a town or two to stop. And that is true no matter which route you take.
If you have an interest in forests and nature in general, the National Park is not something you can visit in one hour.