Actually, Vinylex is a general purpose vinyl, rubber and plastic dressing. It work equally well on the interior, exterior and under the hood. If you're looking for a "true" plastic cleaner for clear plastics, take a look a Plexus (
http://www.properautocare.com/plexus.html).
Interior cleaning: there are a lot of good products for cleaning the interior plastic and vinyl surfaces. Lexol cleaner works pretty good, as does Eagle One. I use the
Pinnacle cleaner (
http://www.properautocare.com/pin-250.html) on most everything because it leaves the least residue. I recommend cleaning with a cleaner every 4-6 month (depending on your use of the car). Wipe down the interior with a damp cloth every time you wash.
For application, I recommend a simple foam applicator pad.
db