Which profession to choose? (cost vs benefit)

Something I've been thinking about recently is juggling around crafting skills on my alts on my horde server. On my alliance server, I had better knowledge of the game, so I was able to plan which alts would take which skills in what order so that I could get the best benefit. On my horde server, I have picked them, dropped them, juggled them around, and in the process wasted a LOT of time and resources. For example, my main (a prot paladin) has been a miner, blacksmith, jewelcrafter, enchanter, and miner again.

I hopes of sparing people those problems, I have decided to give a short overview of the professions from a cost benefit perspective with which classes gain most from the profession.

Alchemy - Alchemy takes herbs and turns them into various potions and elixirs. It also has the ability at higher level to transmute materials. It is most effective paired with it's gathering skill Herbalism or Inscription, another crafting profession that also makes use of herbs. Any class can benefit from alchemy.
Cost - 3: herbs have become slightly inflated recently, but it doesnt take many per item
Benefit - 4: anyone can use the potions and many have uses in other crafted items

Blacksmithing - Blacksmithing takes materials gained from mining and turns them into weapons, armor, other useful items. It can be extremely painful to level through vanilla content with expensive materials and a lot of them required. However, this pain eases in TBC and Wrath, making blacksmithing a lot more useful. It is most effective paired with mining (it's gathering skill) or jewelcrafting. Plate wearing tanking classes gain the most from blacksmithing (paladins, warriors, and death knights).
Cost - 4: Thorium is the most expensive/rare crafting material and BS' need a lot of it
Benefit - 2/4: If you wear plate, its pretty darn useful, if not, don't bother

Enchanting - Enchanting is a unique profession. It has no gathering profession associated with it, it gathers it's own materials by breaking down green or better items. It is therefor VERY expensive from a cost perspective, but the benefits it grants are permanent. It is most often paired with tailoring another profession without an associated gathering profession. Any class can benefit from enchanting, it is easiest for classes that can solo instances to gather low level materials.
Cost - 5: Most expensive profession in the game at any given level
Benefit - 3: small boost to stats, can be used on most item types and permanent

Engineering - Engineering creates ammunition and random gizmos. It can give an increased utility to most any class (lockpicking, resurrection, invisibility and teleportation) that mimics abilities from other classes. It is most often paired with mining (it's gathering profession). Hunters gain the biggest benefit from engineering as they can make use of all of the gadgets and great benefit from scopes.
Cost - 4: see blacksmithing
Benefit - 2: lots of gizmos anyone can use, but marginal actual utility

Inscription - Inscription gives the ability to make glyphs scrolls and a small selection of items. The glyphs benefit all classes as do the lower level shoulders from card decks. They can also create off-hand items for casters. It is most effective paired with it's gathering skill Herbalism or Alchemy, another crafting profession that also makes use of herbs. As most items from inscription are BoE, most classes will benefit from it equally.
Cost - 4: Uses LOTS of herbs, but not quite as expensive as enchanting
Benefit - 3: glyphs improve performance of abilities, sometimes greatly

Jewelcrafting - Jewelcrafting gives the ability to make rings, necklaces and at higher level cut gems for use in sockets. The gems are a great way to customize socketable gear and the jewelry is a great boost for leveling in older content. It is most effective paired with mining (it's gathering skill) or blacksmithing. As most items from inscription are BoE, most classes will benefit from it equally.
Cost - 4: Uses less metal than blacksmithing or engineering, but gems can be pricey
Benefit - 3: Not all equipment is socketable, but great benefit when applicable.

Leatherworking - Leatherworking gives the ability to make leather/mail armor and specialty bags. It is of unparralleled benefit to classes that can wear the armor it can create. In a lot of cases, the crafted armor is the best at a given level. It is most effective paired with skinning (it's gathering skill). Shamen, druids, hunters, and rogues benefit most from leatherworking.
Cost - 2: most leather and hides are terribly deflated and this assumes
Benefit - 1/4: very minimal if you can't use the armor, one of the best if you can.

Tailoring - What is one thing everyone in the game needs? Bags. Tailors make bags and an assortment of cloth armor useful for casters. It is most often paired with enchanting another profession without an associated gathering profession. Casters benefit most from tailoring.
Cost - 2: most leather and hides are terribly deflated and this assumes
Benefit - 3/5: Everyone needs bags and for casters this is hands down the best profession.

The winners? Leatherworking and tailoring for sure if you can make use of the crafted gear for sure. Alchemy also has a clear cost benefit. Blacksmithing brings up the rear if you are a plate wearer, but I can definately understand if you want to skip out on the painful leveling process. I personally wish I had never dropped it on my paladin (although jewelcrafting has been useful).

The losers? Enchanting and engineering. One provides a small benefit but will kill you in the wallet, the other provides questionable benefit and is only slightly less painful cost-wise.