It's probably done in part for the sake of other people in multiplayer that you're doing something and not just AFK. I can agree that combining the animation into one which triggers upon casting is a good idea.
Perhaps when deciding what spells to cast, a slight shift in stance and a glow would suffice as in indication.
I hadn't thought about the multiplayer aspect, as it's not my thing; but even in MP, I would think that any preamble animation should be subtle as each player will often try out many different options, which could become quite distracting/messy.
