How to translate 目的性？
性, in this context, means 有...性质， having the characteristic/sense of ...   

So, 目的性：有 目的 性质， 实用性： 有 实用 性质.

You could translate 性 according to your contexts, and sometimes you could even ignore it when you feel it's unnecessary. It's all at your own discretion.  

In this context, I suggest using noun words, like 实用性: practicality, 目的性: purposiveness. And purposiveness is the same as "sense of purpose".  

有更准确的目的性。could be "be more clear/precise on the sense of purpose/purposiveness".