For what it's worth, flexible materials don't last forever. The worst would be latex rubber that masks used to be made of-- it lasts for about 10 years. Other flexible materials, like silicone and polyurethane have a much longer lifespan; maybe 20 - 30 years? I have some cast-skin (polyurethane?) godzilla toys that are more than 10 years old, with absolutely no hint of deterioration (and I don't do any maintenance on them). Ultimately, I don't think that you can really do much to avoid deterioration though. Armorall helps protect vinyl dashboards from drying out-- they're subjected to some pretty severe conditions. I don't think that it can fully replace the plasticizers that naturally leach out through time, or indefinitely stave off the natural deterioration of the material.
If you've got the time and it makes you feel better, go for it. Otherwise, enjoy the toys now for their coolness factor. In 30 years, you may not even care!
-Jim