I just bought 303 aerospace product to clean the vinyl and realy like the finish. I cleaned my leather seats with Meguiars cleaner and leather protectant but leaves a dull shine. So, I finished it of with the 303 aerospace protectant. I figure the meguiars will soften the leather while the 303 will protect it. Am I correct with this reasoning? Any thoughts?

I've never tried combining products on leather, but I don't see it as being a problem.

The only issue is how the 2 products react to each other. That's an unknown. You'd be better off using a single product for conditioning/protecting. If you like both products, use them on alternating months.