Lee, if you stick with Meguiars stuff you can go wrong, any of their trim cleaners etc word fine IMO, I dont use autoglym products at all anymore, there are cheap and cheerful and always leave a less than satisfactory finish on anything, whether it be painted panels, glass, trim or interior..

Don't fuck about with peanut butter for fuck sake! Use something that is meant to do the job!

Furthermore, to avoid it in the first place (rather than apply something beforehand as someone has stated) just mask the area's up with tape, that way you can do things properly then!

Finally, if you want to paint things to avoid this then i think it's a good idea, on my old Saph I painted the front plastic scuttle, Mirror Bases, Dorr Handles, Rear 3/4 sails and C Pillars all in Matt Black, trust me it looks the tits!