I have spent quite a bit of time in detail forums, and that is one of my "vices" as well.
The pros tend to shy away from Armour-all since it is petroleum based (ie you could rub motor oil on your fenders and make them look shiny, but not very good for the long term life of the plastic)
Mothers works well, but I find the way it gets applied can be a bit of a PITA, and is kind of wasteful.
I have used this stuff on the plastic on my '01 Escape and it takes about 2 mins to apply, and is about $3 USD @ Wal-mart.
spray it on and wipe any over spray or excess with a MF cloth 2 mins later and yo'll have weeks of shine. Beyond that, Lexol vinylex a more powerful petroleum free protectant:
, and 303 has a UV blocker in it, as sun is the biggest proponent to plastic degradation.