Mike, your analysis of the benefits of silicones is the best and most accurate series of write-ups that I have read in an automobile forum - ever! For those non-chemists in the forum, READ what this guy is telling you - the root cause of your problems is not silicones - or petroleum distillates (oils & solvents) - or waxes... It is the fact that you have sun-drenched, old plastic/rubber - that has reached its useful life... No matter what dressings you apply to these surfaces - they were destined to crack/fail due to years of exposure to sun/weather.

Also, please realize that these dressing are really very thin surface coatings and their ability to extract/affect the underliying plastics is almost non-existant. They really just lay on the surface and provide shine (from the oils such as silicones), less-shine (due to drying/matteing agents, such as other polymers) and uv-protection (if those ingredients have been added to the formulation)... That's it...

Lastly, I've used silicone sprays, emulsions, even straight siloxanes on tires & plastics for 32 years (before Armor All existed) and have never experienced or read (in technical journals) of a negative affect of silicones due to their use on the surface of rubbers or plastics.
As Mike states - this does not mean that you want to apply paint to a siliconized surface - but just use them for their intended (and limited) purpose in these dressings - which is to impart a clean, darkened, shiney surface to the rubber/plastic.

Hope this information helps...