For me, a general rule would be to never have more than $1,000 in a mobile wallet, and I don't think I've ever had more than $500 or so. The rest is in cold storage. I haven't ever had any problems, I haven't been hacked or anything, but just because it hasn't happened doesn't mean that mobile wallets are secure.
I agree with your personal decisions of not leaving amount above $1000 on your exchange wallets, this may be hard for someone that is an active legendary trader with some good amount on their exchange balance for trading, and likewise some others that find online wallets easily accessible and flexible, this is why we most times decide to divide our assets into several categories.
Cold storage is for long tearm assets for me bitcoin and the rest, i have some good amount also on online wallets but that is for some purposes, like trading, purchasing goods and p2p transactions.