I only have an Incase Snap case over my iphone 5 and I carry my phone in my front pocket. It gets used a lot. There's almost no weight penalty. If it were to rain, it would go into a ziploc and maybe into my pack. I never buy insurance for electronics – new models come out often enough that I would just get a new one if needed.
If I were carrying an iPad, I'd have a similar case – ie no impact protection. If anything, I'd slip it inside a ziploc bag which would then get wrapped in some clothing.
Mike

