Counterparty is not a side-chain.
I like the way they added blockchain functionality. What they did was to allow users to tokenize their cards, which then allowed them to exchange them for BitCrystals (BCY). The game itself is not using any blockchain. It is only using it in the process I just explained to you.
As most users would not be exchanging their cards, Bitcoin block producing time makes no difference on the gameplay itself. You could be playing, and if you improve some card a their maximum level, then you will be able to tokenize and exchange it. That doesn't make the gameplay slower.
I don't see any need for any app to use Steem. Only those which create consumable content, like Actifit does, are in the right direction. Steem allows apps to store arbitrary data in the custom_json transaction kind. But that doesn't mean they must. Doing it just because they can doesn't add value to the Steem tokens and are only a "feature" to attract more people.