The different options have to be balanced in value, giving a skill boost AS WELL as the advantage of having the car, would make it outweigh the other options.
If you're not talking about a boost in character skills, why did you say "skill boost" and not "value of the car"? Seriously, using the term "skill boost" makes it sound like you want some boost to security and/or driving skills, ON TOP of giving the player a sports car, just for picking that option. That makes the option too over-powered and devalues all the other options.
If you're talking about making the car a lot better than what you can normally steal, that just means all the other options will have to be upgraded to match. e.g. a sleeper lawyer or $1000, are they "just as good" as your idea for the car?