well bought a speed pack rear boot spoiler, new but not my car color which is black, it was half price, so think got a good deal, anyway was going to get resprayed, but cheaper option is wraped. Tought of black carbon fibre effect, would this look strange, when no other parts are done, or just get done black

 

I dont understand the cheaper option statement, but anything that looks carbon fiber on a car only makes it look more sexy and exotic.
Remember, the avg person or uninformed individual doesnt know to give a damn, but the person who dreams of having carbon fiber on his/her car will envy you until you are out of sight.
Carbon-fiber on a jag only makes it look more avant garde and haute coutre (Did you mean wrapped or warped?).. Dont wrap it cause you will look like a hoodrat

 

Since there are no other matching parts on exterior i would avoid the carbon wrap personally. Would have it painted to match. Unless you carbon wrap some other parts of car to make it tie together maybe? I personally like speed pack kits painted to match

 

the spoier was over £250 to buy,,i got for £100. I can get it wrapped for £50 in colour black to match car or black carbon fibre, alot cheaper than painting, think black as you say, have no other parts on the car that are carbon effect, it has chrome details everywhere else so black may be better

 

Paint unless you have carbon to match. I have a carbon rear R-S diffuser on order but have to install a few other carbon bits to it matches or it will look tacked on.

 

Check out Hydrographic Coating of the spoiler in a Carbon Fiber Pattern if that is what you desire with the end look and appearance.

If the item is a carbon fiber spoiler in material only, not finish or look, get it painted to match the car.

 

I think matching black will look better than CF, unless you're planning to add a load of other CF details (mirror covers, vents, etc.).