I've only used plastic dip on small items and I don't see how it could even look halfway decent for very long on a complete vehicle. I'm an auto body shop owner so I'm always keeping up on new products that will have long time durability on customers vehicles.
Flat clear coats have less uv protection for your base coat because of the flattening agent that is mixed into the clear so it will wear over time, and be less easily repairable.
Shiny finishes depending on the clear coat quality will hold up better because you can sand and buff small scratches and also spot repair them. You can also wax shiny clear which makes the surface easier to clean.
Is plasti dip being sold in large quantity like qt and gallon size or just spray can size?