First off, this would clearly only work properly if it's possible to stack things according to enchantment value like you can damage value (I.E. Wool) but I think it would give people another element to spend EXP on that's not strictly combat related, and saturate the game with more adventuring options and building aspects.
Granted, you probably should enchant a whole stack all at once, even if the enchants end up being on the cheap scale.
So let's start with the food, some of these are made to preempt a big fight, or give adventure map makers a better throttle on food choices; making players have to choose when to eat big effect foods.
Fulfillment : Grants the opposite effect of Hunger, slowly restoring food level, roughly +5 seconds per level of enchant. Eat this, then go into that giant room full of nasties to counteract the food losses of combat.
Stuffed : Boosts the food's saturation level.
Cleanse : Removes status effects Poison and Hunger
Purify : Removes... other... uh, status effects... for future use? Including a list value for easy flexibility. Curing potion effects seems a little too powerful though, stabbing zombies for a consistent gain to counter variable resource farming? Eh.
Hearty : Rare enchant; Gives, well, hearts, it heals you a point per level of enchant.
Sparkles : Rare enchant; Filled with joy and fairy dust and probably doesn't make you a vampire. Also don't know how well the game takes to a moving light source because I haven't tried that torch mod. But yeah, that's the general idea.
Block enchants; these are made to make your creeper shelter stronger, your garden grow faster, and probably another hundred things I can't think of off the bat because I'm not batty enough, er, creative? Nah, probably just don't spend enough time playing MC to come up with a greater degree with things you could enchant blocks with to make the world a little more detailed.
Blast Resistance : Increases the blast threshold of the block, maybe not up to taking a point blank TNT/Creeper blast though at the highest rank.
Enchantment <color> : Tints the enchantment color, probably using RGB, including a transparent version that makes it look like the block isn't enchanted when placed.
Redne-on : I'm sure there's a more clever name for this, but the idea is that an Enderman can't pick up the block, and attempting to/touching the block will force it to warp like if he touched water instead. A must for mineral blocks.
Light / Darkness : Okay, so I don't know if this would even be feasible to do, or in Darkness's case, possible, but the idea is that the block becomes an emitting block that adds or detracts light levels in the spaces around it depending on the level of enchant, this way you don't need to rely on obvious torches or oft mismatching glowstone to detract from your buildings, or reduce the effectiveness of placing torches around user maps with darkness.
Chipper-Proof : Mostly just so you don't accidentally pull up a block on accident because your diamond is just too strong, or just a sort of delay toward goals, doubles the time to pick a block, like you were underwater.
Nourishment : Dirt only; Decreases the time it takes for crop to grow on the block. Double purpose with removing the ability to convert to a grass block.
Gravity : Toggles blocks to act like sand, and sand... not... like... uh, sand. Might take a bit of an overhaul to give active/inactive flags for all legitimate blocks...
Everburn : Mostly for Wood/leaves/etc, makes them burn similar to Netherack.
Inconceivable : Rare enchant, Sometimes when placing a block, it won't take one from the stack. Not enchantable on mineral blocks (Iron/Gold/Diamond/Emerald related) for obvious reasons. (Might be easier if it's made so that if a stack of mineral blocks would be enchanted with this to be enchanted with Redne-on instead.)
Sunny : Rare enchant, another one I'm not sure is directly possible without some rule tweaking, but effectively makes 3/5/7 blocks away from the block periodically burn undead as though in sunlight. Should this one glow and cause max light in effected area? Probably.
I believe that the enchantment you have for the dirt should be on the hoe itself, this is because when someone places a dirt block down, that does not necessarily mean they are going to use it as a farming material. Also, if one where to place an enchanted block down, would it emit a purple light like many enchanted items, or will it be like trying to find a needle in a haystack if you accidentally place the block down?