How is it different from a normal one? Does that ability have a "turn on&off" switch that makes it a significant thing? Or like the example listed by Emma Collidge, in which the user can make a difference or effect something physical or the enviroment related/utilizing this ability?
Enhanced Synesthesia is presumably any form of synesthesia that benefits the user. Smell percieved as sight makes the user an excellent tracker. Sound percieved as sight can be used for echolocation. Electroreception percieved as any of the basic 5 senses can enable the user to sense electricity nearby, which ranges from cell phones to lightning.
Bit late to the party here - It's enhanced because synesthesia, as it's real-life condition, isn't the same as it's fictional counterpart. Actual synesthesia is more so a form of 'involuntary experiences in a second sensory or cognitive pathway', which is just a fancy way of saying one form of sensory input triggers another that is usually unrelated i.e. seeing certain shapes may trigger someone with synesthesia to taste a certain flavour. Where as, the fictional synesthesia (or Enhanced Synesthesia) the person with the condition will to able to accurately make out factual details or a scene instead of just perceiving something on an entirely personal level.
Well, such as in the TV Series "Heroes" - at one point we the protagonistic character of Peter Petrelli acquire an ability that involves enhanced synesthesia. With this, we see objects that make sound (like a trash can hitting the ground) produce light/energy visible to only the ability-holder. At another point, we see a piano seemingly radiate ribbons of colour. When in actuality - someone with synesthesia really only visualises these colours and patterns in their mind and not as radiant energy existing in their environment.
I related it to being able to make out details in a scene because in the example with the piano, the ability holder was a deaf nurse - she could not hear the sounds being made, but she could see them.
"and not as radiant energy existing in their environment"
- Acutally, some people with synesthesia can visually interpret things like sound as flashes of colour in their vision! I found a video that explains this from the point of a musician with synesthesia, if you're interested!