IMO, it is not worth the high hashrate price.
It is worth - when GHS are from refs a sort of ponzi atm but here you do not have to pay anything if you don't want to and at any time you can withdraw everything what you get.
And one more thing - everything can change and this "little" can be worth "something" in the future
Even for the referral earning, it would be better to just sell the GH/s from ref earning instead of mining there.
Anyway is good to have this (even if that's not much). That's in cex.io is the best. You don't need to do nothing. It is just there and is working for you.