Meet the cast...again!
Ok, what's changed...I've discovered a little texturing trick that allows me to put a glow around the characters. Since this is texture based and not light based, it has a relatively low hit on the render. It also matches whatever angle the camera is at, so it's very low maintenance as well. It's allowed me to remove the toon outline shader on the ghost as well, which did impact the render time somewhat: since mental ray couldn't render the outline as it originally was, I had to convert it to polygons. These polygons would then rebuild themselves everytime the camera moved (the shader matches the camera movement so you constantly see an outline: it's more commonly known as cel-shading), which added plenty to the render.
You'll notice that the colours are more vibrant this time round as well: I embedded my LCD screen profile with this image. I'll probably end up batch processing the entire animation with this colour profile, as it gives it a much more colourful feel. At least, on my screen it does.
Now, imagine this at a twilighty/night time setting, with cool cutout trees and clouds and stuff...
The ghost looks a lot better.