One, because I'd need to shape them out of the layer mask and they'd still have a blue aura, from the planet surface. Particle effects are awful to extract from a screenshot, so I'd hate to do it.
Two, because the letters are the top layer (in a look-at-it-way, not what PS shows me) so every other layer is set up so they won't be touched.
Oh, and Exile's sig is awesome due to two reasons: both, the render he gave me (girl with deadly cake) and the background I chose for it are awesome work. I basically was a lazy ass there and created a fusion of two good looking things. If done right, such a process will always deliver a tasty work.