I personally like the Vision GT cars, as it shows futur possibilities and make Manufacturers really think out the box. And in addition to that, many remind me of my Hot Wheel Cars
But to be honest, I only like them in the Gr.X class, as many of them really don't fit in the class.
One example is the VW VGT in the Gr.3 class. One essentiall rule in the GT3 class is to have a roof. And the VW VGT doesn't have one.
And I personally really don't like the VW Beetle Gr.3 as it really looks out of place, as the GT3 class contains Gran Touring (GT) cars. I wouldn't call a Beetle a GT. I would have liked it, if they would have used a Beetle in the gr.4 class.
Also the Citroen concept car really doesn't fit into the Gr.4 class, as its Aerodynamics are really out of place for a GT4 class. Look at that Citroen and than look at the VW Scirocco. That's really weird looking and in Reallife the Scirroco or any other Gr.4 class wouldn't have a chance against the Citroen as it's a spaceship against the other cars. It doesn't fit the rules of the GT4 class.
The complete opposite is the Bugatti VGT in the GR.1 class. Aerdynamic-wise it wouldn't stand a chance against all those highly aerodynamic cars and it doesn't even fit the rules of the LMP1 class.
Things like that ruin the fun and immersion for me personally. That's why I mostly like the VGT cars only in the Gr.X class.
(having the possibility to choose specific cars as opponents would be a benefit for everyone)