I didn't use duplicolor on the rest of the interior bits.
The only things I used the duplicolor on were the carpet and the headliner. I'll watch out for fading and try your suggestion if it starts looking like crap.
For everything else in the interior I'm using mar-hyde satin exterior trim paint. It's meant for exterior plastics so it's tough as nails. It also looks good (to me) as I don't like shiny on most interior surfaces.