Mirror Image could be easily done; make it a standard buff, and simply have a series of ghostly duplicates (translucent to the caster and his allies) with no collision size move close along with the player (opponents see them as completely opaque). These duplicates mimic the animations of the caster. Anything that directly targets the caster has a chance to be completely negated by one of the duplicates (Number of duplicates/number of duplicates + character). If a duplicate takes a hit, it immediately dissipates. Area of effect spells simply hit the player, and dissipate any duplicates in its AoE. This spell would be incredibly useful. Great for negating melee damage, and deadly individually targeting spells.
I think that this implementation would make the spell too powerful unless it had a long cooldown or some similar way to prevent the spell from acting like a stacking Displacement. It has some merit, but may not have any middle ground where it is both useful and not totally over powered.
Colour Spray is obviously a useful spell, especially at low levels. A cone that puts to sleep, blinds, or dazes, and works even on higher HD opponents? Sign me up.
Any spell tied to HD in DDO is pretty much doomed from the start. I like the spell in PnP, but HD scale up too quickly in DDO for these types of spells to be worthwhile--there are kobolds in level 2 quests that would be almost unaffected by this spell.
Project Image could work by switching the player's vantage to an illusory copy of himself which, while only being able to take one hit, has access to all of his items and powers. Upon gaining the spell, the player gains access to a pseudo feat that allows him to switch control between his normal body and the Image. Whenever his actual body takes damage, the damage indicators, red numbers, groans of pain, screen distortion appears as usual. If manual control is not taken of the projected image, it simply mimics your movement and animations and works as per Mirror Image. There must be a line of sight between your body and Project Image at all times, or the spell terminates within 3 seconds after providing a warning (a translucent line could be used to show the line between the image and your caster).
The other Image spells (Silent, Minor, Major Image) themselves could be used to create insubstantial duplicates of a targeted character or creature which can simply draw aggro. Each time a non-mindless monster successfully damages it, it gets a Will save to realize it's not real, whereupon it ignores the image in favour of real targets. You can also manually pilot the duplicate as per Project Image, but you cannot cast anything from it.
I don't think these have any place in DDO. Projecting yourself in PnP comes with many risks, one of which is rarely truly being certain that your real "self" is safe, which is something we really need not worry about in DDO. Also, the implementation would be wonky, as we'd have to have some way of both seeing our real characters and the projection, in addition to controlling it.
To make Ghost Sound more consistently useful, and upgrade it to a level 1 spell (there are no cantrips in DDO) it could not only be used to attract attention, but also daze opponents in its area of effect for one round on a failed Will save, by creating a booming, illusory sound. Useless against "deaf" flagged opponents.
We already have daze monster don't we? Does anyone us it?