See this post by mevaseretzion. He argues that one can increase his own spirituality illicitly by not doing the right thing at the time. Even if another mitzva has more "value" and would push the person to a higher spiritual value, sometimes that person must forgo the added spirituality by doing something else which is necessary. This is one lesson of Mordechai's political tenure.
I agree with mevaseretzion. The truth is mevaseretzion's distinction is similar to the obligation to do mitzvos despite the fact that Torah is of greater importance.
There is a mitzva to shake a Lulav. But if Talmud Torah has the greatest value, then why should we pause Torah learning to fulfill the mitzva of Lulav? Isn't the most reasonable course of action to do the mitzva that is the most valuable? I'm sure there are all types of answers to this question, but the most obvious point is that we sometimes are required to act in ways that run contrary to our obligation to do the most valuable mitzva. Even though by learning Torah instead of shaking Lulav we would be making the best use of our time (by doing the more valuable mitzva), G-d does not want us to do what is most valuable, but rather to do what he commanded.
This logic applied to Mordechai. Rather than learn Torah full-time, he became part of the government, which was imperative to the well-being of the Jewish people. The most valuable mitzva would have been to learn Torah, so he did not maximize his time if we look at the situation purely based on the value of the mitzvos. But our obligation to follow G-d's command and not determine our own value calculus. He makes that decision, not us.