It's a clunky mechanic, but I think it is designed to be the process in which technomancers keep up with everyone else. Especially that registering is free, to me, means that sprites are intended to get lots of use for more typical actions (unlike bound spirits that are more powerful but are intended to be used more sparingly).
For me, the reaction enhancer/sprite combo is a way to keep up with magical/cybered characters (combat sense, reaction enhancers/wired reflexes. improved reflexes, etc.). Adepts and highly 'wared characters can get defense pools so high (especially adepts - sheesh, standard combat mage build - Soft-capped Reaction/Intuition, Maxed Agility with Muscle Toners, Agile Defender, and Magic 5 for Improved Reflexes 2 and Combat Sense 5, they can rain bullets and avoid all but direct magic and AOE attacks). I'm not asking for physical initiative boosts, just a way to leverage wireless matrix information to not get shot as easily.
I would be ok with ambient Noise penalties affecting these bonuses too, and think it would make technomancers more dynamic, recognize their powers are more contextual, and be conscientious of the wireless signals around them. ("Hey guys, don't expect me to Neo it when we are on that submarine".)