Only reason to do this would be for your own enjoyment which is a good enough reason as any
Glass and carbon as island911 correctly pointed out create an unbalanced laminate which could cause distortion. I couldn't say by how much as it is very dependent on the shape, ratio of carbon and glass, type of weaves, stacking sequence and fibre orientation of the laminate
I've used this combination of materials to create a temperature dependent morphing structure on a F1 car, was very effective at creating deflection but in practice didn't add any car performance so the idea was dropped
As both your ducktail and hood will have an internal structural frame and the added carbon fibre content won't be much I'm not sure you'll notice any distortion problems. If you're going to have a distortion problem it will be on the hood as it is the larger part with the least shape to it. The ducktail may get hotter but it's smaller and has a stronger, more self supporting shape. I'd suggest doing the hood first as it should be the easier than the ducktail.
I think making the un-moulded external surfaces shiny and smooth will be your biggest problem
The uni-directional engineered laminates island 911 refers to only really work on large curvature parts such as aeroplane wings etc. Uni-directional materials are frequently used in automotive/motorsport but are always mixed in with woven fabrics. This added complexity is not even worth considering for your project.
I'd suggest using a woven 200 gsm 2x2 twill for drape-ability, cost and looks. A heavier fabric would work but won't wrap well around the panel edges. Also use a UV resistant epoxy resin if you can as it will be more durable than a polyester resin and should give an improved adhesion strength between the carbon and original fibreglass. Very important also to well abrade and degrease your f/g panels before laminating on the carbon. Something like a 400 grit wet and dry should be fine.
Please post up your progress as I'm interested to see how you get on