I tried the silicone spray with the '96 Odyssey, exactly as you suggest at every oil change. It made absolutely no difference in the longevity of the CV boots. They failed at about 8 years and 120,000 miles just like every other Honda and Nissan I have owned. There is anecdotal evidence, especially with the Nissans, that prophylactically replacing the half shafts when the joints are still good can reward you with an unbalanced axle. It is not a given that just because the boots are torn that the joints are automatically bad. It depends on how long they've been torn and what sort of driving has been done while they were torn. If you caught it soon after the tear happened, and it hasn't been submerged in water or slush or pounded with dirt roads, most likely the joint is still good. I have never replaced a boot until it tore, and have never had a joint subsequently fail. The mechanics like to replace the whole axle because its less work than doing the boot, not because its better.