Trading mining is actually a small bonus to you for trading operations on this exchange ,and it is certainly profitable if you are trading there or are going to do it ,but everyone decides for themselves whether they need it or not 
There are few bonuses. Some of the coins has volume mining, some of them market making some of them has both. Idena has market making bonus ... it means that you earn by leaving an open order as long as possible in mining range area. Idena is currently in top 5 most traded coins there and has x3 market making bonus - the only coin with such bonus. I hope it will boost liquidity there because despite 1 whale who is placing 0.25 - 1 BTC walls and guys filling his bag with taker orders there is one else.