To me, I love sun faded cars. I do not want my cars to look like toys or new cars just out of the shop, I want them to look real. The matte finish spray is a bare minimum effort to make the cars look real, knock down that toy looking shine. Real cars can be sun faded. A sun faded car is a great start for a weathering project and I love weathered cars. That is part of what got me into G railroading many years ago, saw a weathered G car being ran on a layout at a Christmas flea market and it looked kinda like a real car shrunk down and I got interested in doing it for myself. The rest of the cars being ran had no weathering and the difference was stunning (unweathered cars looked bad in comparison).
Some years ago, bought a Bachmann tipper ore car that had been in a hobby shop window for some years and had faded and also got a sag on one side on the tub from all the sun. Made it look like some damage from use. Made a good custom car candidate.
I guess i should suggest that you guys stick to your pristine cars and save the faded and abused ones for me.
Doug