Matt,
You still, I think, are missing the larger point. Most of us will agree that solvent/silicone based dressings aren't the best thing in the world for tires, and I tend to stick with 303, Vinylex, and other PDMS formulations myself. Most of us are also aware that migratory silicones can be a Bad Thing<sup>®</sup> in a paint shop environment.
Now, all that said, MOST of us go through tires quickly enough that dry rot is never a problem. Hence, solvent and silicone in dressings is much less of an issue, if one at all, for those of us with daily drivers. I'd wager that for > 99% of us, tire sidewalls cracking or failing for any reason prior to the tread being worn away is a non-issue. Of course, as you point out, garage queens or classics that don't see much road time may have a real concern, but for the rest of us flogging the daily driver around town, it's highly likely that we'll run out of tread long before any sidewall damage from silicone, real or imagined, should appear.
As for using wax or sealants that contain some amount of silicone on your paint, I've not seen any research presented here to indicate that silicones are harmful to cured paints. To my knowledge, they're only a problem in a body shop environment where re-painting is taking place. If a body shop isn't competent enough to clean panels of all traces of wax and sealant before painting (regardless of whether the wax/sealant was silicone-based), I don't want them anywhere near my car with a paint gun.
So, use what you like. If you're happier using what you believe are silicone-free products, then by all means, continue to do so. However, the warnings in mulitiple threads of the dangers of the evil silicone monster, when there is no major body of evidence (marketing blurbs notwithstanding) to support the premise, sounds more and more like the sky is falling.
Tort