Peregrinos,
Having now done the trip, I need to report back. We walked out of Sevilla and it was a lovely walk. It takes virtually no time to get out of the city. Cathedral is about 10 minutes from a bridge to Triana (this is a lovely old town, not a suburban wasteland), quick walk across (maybe 20 minutes), another bridge, and then you turn and walk along the river past fields and grazing horses (and a two-horse team pulling a wagon!!) before turning and walking mostly gravel roads to Santiponce. Short 10K for the first day (since we started at 6pm--sightseeing. The Alcazar is out of this world).
So, even for those like us, who do not share the "every step approach," this is not a city to take transport out of. I appreciate all the disciples of that denomination who have attempted to convert me. I regret to report that you have failed, but such an approach is good advice for Sevilla (once you've walked out of Granada, we'll continue the broader discussion).
Buen Camino,
Jo Jo