One thing I think I'll add to the elemental magic of the Dragon Blooded is the concept that an elemental magician must attune him or herself to the element that they wish to control, and that this process brings with it detrimental side effects.
I want this kind of magic to have some down sides because it is more immediate and versatile in many of its effects. Sorcerers have to find spirits, bind them, and then deal with them. The Guild magi have to create their effects and tools in advance. The ceremonial magic practiced by the Church requires both time and typically a group effort to initiate. Whereas an elementalist can call upon his or her chosen element once the necessary power has been channeled.
Attunement is a concept I've seen in several places, so it's hardly completely original. But a lot of fantasy elements keep reappearing.
Anyway, here are the bad side effects associated with each element:
Earth--Body becomes particularly fertile ground for various microorganisms, highly susceptible to various sorts of fungal infections on the skin, produces a ripe smell due to bacteria. On the plus side one can digest almost anything.
Metal—Bones turn increasingly metallic and heavy, causing unpleasant stress on muscles and tendons. Basically move more slowly much of the time, endure chronic pain--can get so bad that limbs are voluntarily amputated. Unlike real life, the metallic bones don't result in blood poisoning. On the plus side, very hard to break a bone.
Fire - Body temperature rises, renders the elementalist sterile, physical dehydration and associated bouts of delirium a problem. On the plus side, quite resistant to cold and warm weather won't cause any worse effects.
Lightning—Body’s electrical impulses become irregular, leading to uncontrolled spasms and twitches; body may also radiate ions during bad moods that make nearby people uncomfortable and edgy. On plus side, can produce a pleasurable electric buzz in others.
Air- Bones become brittle and fragile and body loses mass in the form of lower density. The elementalist becomes less physically strong because the bones make for weaker levers. [Note that the Dragon-Blooded still has heightened stamina and healing abilities.] The positive is that the aerially attuned have beautiful speaking and singing voices as well as exceptional breath control.
Rain—Emotional moods generate highly localized, very minor weather effects (little clouds, fogs, mist, frosty breath, etc), making it very hard to conceal one’s feelings. On the plus side, the rainmaker can always stay cool in the heat.
Water-- Become cold and clammy, take on more water weight, get heavier, move more slowly and clumsily on land but swifter and agile in the water, like a sea lion.
Wood—Must spend longer and longer periods in a physically dormant state. On plus side, less need to eat.
I'm also thinking about giving a particular flavor to the Noble Dragon-Blooded magic based on which the three Realms (West, North, or East) that the Noble House belongs to, similar to how the Guilds in each Realm focus on different applications of material magic, but I haven't really figured that out yet.