Spirits in the Material World

Under Oriental Adventures, Hordelands/Mongolian analogue, Spellbound/Faerunian E. Europe analogue, and probably also Anchorome (North America analogue, esp. the Pchughstick/NW Coast stuff I'm working on), the "Spirit" subtype includes all outsiders, fey, and elementals.
The purpose of the "spirit" subtype is purely one of mechanics, since certain classes/spells/etc. (e.g. Spirit Shaman in 3.5) deal with creatures of that subtype, and it is meant to fit the shamanistic/animistic view of spirits. In reality, it's not all that complicated.

While on a similar subject, IMO the element systems for the Shugenja and Wujen need serious work in order to actually resemble the Far-Eastern view of the elements. Particularly, they do not resemble the traditional view of the elements, though to be fair, I think going with the modern Japanese view of the elements, melded with the western elements would be far preferrable (in most games, anime, etc., the 5 Chinese elements are recategorized into the western elements, with electricity and metal becoming earth and wood being lumped with wind, as it generally is in Japan. I know little of the modern Chinese or Korean view of the Chinese elements, sadly, but the Japanese one tends to closely mirror the modern Western view as opposed to the antiquated view-- that is to say, wood and wind are viewed as feminine like a woman's grace, whereas in traditional western and Chinese elementalism, both were viewed as masculine. Likewise, metal/earth are today viewed as masculine due to stone's hardness, immovability, and durability when traditionally both east and west viewed earth as feminine and 'passive'. Traditionally in eastern elementalism, Metal was viewed as gender neutral.)
One of the biggest differences in eastern elementalism (modern at least) is that wood is associated with the element of wind instead of earth, due to the blowing of cherry blossoms, fallen leaves, dandelion seeds, and fungal spores, and in fact there really should be some spells related to such phenomena.
Another major difference is that electricity in modern e. elementalism is usually associated with earth instead of air, due to metal's conductivity. Sonic spells (at least some) would also fall under wind/wood.

The more abstract qualities of the elements would require a significant overhaul, sadly.
As I recall, the elements have the following abstract qualities:

FIRE: blindness (assoc. with flash and light), infection/fever/erythema, passion, bomb/explosion, light/glow/shine/illumination, bears, crows, swallows *though modern elementalism associates swallows with wood/wind, and I believe the association of crows w. fire is the same as in NW Amerindian myth-- the crow got blackened in a fire* desiccation, annoyed/frustration/irritation/irk, phosphorus, nothing/empty, violent/extreme/strengthen

WATER: blindness (assoc. w squid ink), wisdom, law/rule/principle/method, peace/to calm, cure/heal life/resurrection, wish/demand/request, dwindle/decline, performance/act/play, extinguish/cancel, deep/intensify, satisfy/full, violent/excited/agitated, oil/fat, purify/cleanse/exorsize, plan/scheme, float/buoyant, dirty/polluted/defiled, stagnate, astringent, abundant, darkness, slippery, frivolous/shameful/shallow/superficial, conceal/hide, dissolve, tears, cry/weep, sympathy (not finished with this yet ugh)

COLD/ICE: weak/frail, omen, congealed/stiff, weird/uncanny/horrible/threatening, clear/serene, skillful, wither/droop/lame, cruel/strict/severe/ruthless/merciless, fear, dependence, mockery/taunting/surly, unfriendly, indifferent/aloof/reserved
METAL: poison, blindless (assoc. with glare and flash), sharpness, money, chain, take warning from/learn from, mirror, dull/slow/stupid/blunt, confuse/mix/be in disorder, discipline/train, refine/polish/temper, respect/revere, needle, be charmed/captivated, lock, massacre/annihilate, a weight, rust/corrosion

EARTH: augment/promote/increase, mould/shape/model, wall, pressure/push/oppress, tenacious, temple, strict/solid/tough/hard, salt, crash/fall down, jewel, resist/endure/withstand, degenerate/descend into, trench/ditch/pit/hole, break/demolish, hesitate, divination sign, collapse, dirt/grime, polish/sharpen/grind, stiff, magnet, obstruct/block/deter

WOOD: fear, poison, echo, worry/concern, fear, arts/performance, authority/power, investigate/examine, plan, reward, succeed, music, comfort, talent, imitation/copy/mock, seal/mark/symbol, abandon/discard/sacrifice/reject, prosperity, honor/glory, design/build, tender/weakness/soft, wither/dry up, decay/rot (oh gosh is this one ever not finished yet)

WIND: insanity, headache, elegance/grace/refinement, strange/eccentric, common cold, appearance/style, message/communication, flying, floating, vortex, sudden/quick

That up there is just the raw results/prewrite.

For the final product, I would recategorize the Shugenja elements thusly:

AIR: travel and movement, speed, influence/charm, vegetation, communication, insanity, sonic, talent, the arts, music, illusion, cunning/scheming, charisma, freedom

EARTH: destructive, resilience, resolve, endurance, protection, gravity/pressure, discipline, electricity, the grave, imprisonment, binding, symbols/runes/geometry/magic circles, animals

FIRE: destructive, blatant, passion, desiccation, light, strength, regeneration/renewal/resurrection (which also falls under water)

WATER: destructive, healing, cleansing, dispelling, exorcism, wisdom, skill, serenity, peace/calm, time, temperance, weakness and frailty, transformation, darkness

Looks fairly balanced to me, although water and earth might be slightly better than fire and air.

In The Golden Khan of Ethengar, a gazetteer for the Basic D&D game, spirits were entities from some other plane whose plane (the Spirit Realm) was brought into permanent conjunction with the Prime after a great cosmological disaster, now existing coterminously with it. The spirit world can be visited by shamans.

In the 2nd edition sourcebook Shaman, spirits are personifications of nature, animals, ancestral spirits, primal fear (bogeymen), dreams of things as they might have been, or other qualities that are actually created by the beliefs of mortals. According to On Hallowed Ground, if enough people worship a spirit, it can become a god, and many of the major pantheons are said to have begun that way. Shaman says that spirits appear and disappear as if they're entering and leaving a parallel spirit world, and they even claim this is what is happening, but in reality the Spirit World does not exist.

In 4th edition, "primal spirits" were created by the world itself as a sort of immune system to defend it from the war between the primordials and the gods. They include spirits of the mountains, winds, animals, plants, ancestors, and so on, but they're distinct in that they're entities native to and personifications of the material plane, whereas gods are native to the Astral Sea and primordials to the Elemental Chaos. A number of entities that were defined as gods in previous editions (for example, the Great Mother of the Moonshaes and Nobanion the lion lord) are defined as primal spirits in 4th edition.