All of the above might be true, but ask yourself if an extra 50hp on a Cure really makes a significant impact either? If any of it goes into overhealing, it's completely useless. Healing up 2000hp with a 1000hp/cure or a 1050hp/cure is still 2 heals either way.

The point is your WHM isn't going to be obsolete if you choose spell speed. Spell speed and determination are BOTH viable choices. People championing one over the other need to realize this.