I used to use 303 on an older vehicle of mine that had that typical mid 80s vinyl paneling that was kind of puffy because it had a padding underneath it. It was very much a more traditional vinyl product that had that fake leather texture to it. Well, what I'm getting at is that it was basically a smooth material in red and looked great with 303 applied.
The dash and other parts of the Prius interior are not vinyl over padding with a smooth texture. These items are hard plastic with advanced finish treatments to give them matte appearance and what I would descirbe with regard to the door panels and the glove box covers as a silky texture, to the touch. My point is that I used 303 in my older vehicles because the materials were subject to cracking because they were flexible and there was stress placed on them in their installation and they could dry out and be affected by the sun.
Hard plastics shouldn't suffer from the cracking problem that soft vinyls do. Because of that, the need for protectant materials is significantly reduced. I cannot find a place in my Prius where I would use 303, especially not on the dark plastics of the dash area.
A product like 303 is going to streak on these materials, where it wouldn't on more common vinyls. I know you aren't going to like hearing this, but I think that 303 isn't going to be of much use on your Prius. I'd put it on the shelf until you find a car with different interior trim.