Personally I'd ITT into Madrid, screw this stupid parade nonsense. Bola del Mundo in stage 20, an intermediate stage into Ávila on 19, a flat stage 18, Alto da Torre on 17 after a flat 16 - this would then mean I could have stages 14 and 15, on the 3rd weekend, in the mountains of Asturias.
I'd also have, instead of a prologue, a circuit race in Ceúta with a climb in it, a week 1 stage over Haza del Lino via Rubite then a descent finish, an MTF on the Coll de Pal in the Pyrenees, and somewhere in week 2 stick in a stage from Jacá to the Higo de Monreál.