I'm looking at getting a 6.3:1 Curado for cranking (because they don't make the 5.5:1 for lefties). Some of my applications will use deep diving cranks while others will use shallow. I want mono for shallow and fluorocarbon for deep. 

 

First, can the Curado spool be changed out without any more difficulty than re-guiding the line? Second, do they sell extra spools? Third, for those who compete do you find it worthwhile to change out line like this or does it take too much time away from fishing? Let's assume you have one rod dedicated to crankbaits and your other rods need to stay with their purpose.

Nope, the spools are easily swapped out and line reguided.  Yes, you can order extra spools for them from Shimano.  I find that it takes about 2 mins to swap, reguide, and tie on a bait.  Not a big deal if fun fishing but I find that's two minutes I could have made 2-3 more casts that could have potentially get me a key fish.