I also agree that less is better and it is nicer to group places that are near by in the same trip. I try to minimize my one night stays and usually have a couple of 3 night stays during a 2 week trip.
For this reason, I'd save Barcelona and Girona for another trip and group it with Green Spain. I've been to all of these places and they are wonderful but they really deserve the time. I would definately visit Sevilla. The weather in the south will be much nicer also in March. Dropping the northern part of the trip would also mean you could spend more time in the sherry towns and white villages and even Granada. I honestly didn't know what to expect on my first trip to the sherry triangle and wasn't expecting much but it was beautiful people, food, country and of course the sherry!
In Sept/Oct 2001 for my first trip to Spain I put together a trip for 17 days that flowed pretty well....not too rushed and very doable with public transportation. If I recall it went something like this:
Day 1 - arrive Madrid; immediate head to Toledo
Day 2 - Toledo
Day 3/4 - Segovia
Day 5 - Salamanca via Avila daytrip
Day 6 - Salamanca
Day 7 - Salamanca to Madrid; AVE to Sevilla via Cordoba day trip.....this was the only day that I traveled more than 3 hours in one day
Day 8/9 - Sevilla
Day 10 - Arcos via Jerez de la Frontera daytrip
Day 11 - based in Arcos drove around the white village route stopping in Zahara and Grazalema
Day 12 - Ronda
Day 13/14 - Granada
Day 15/16 - Madrid (flew from Granada to Madrid)
Day 17 - home
After this first taste of Spain I haven't been able to get enough....now I visit twice each year in April and late September. It is such a beautiful country and each area is unique and deserves time dedicated to it independently.
Hope this helps...