The Korx personality may be Evil, though they really should be played as Neutral.  The extra trade routes are a boon and will more than earn you what you may have gotten as Evil, as are the improved relations.  Also the Korx, especially in TA, are a bit weak overall, and the boosts that you get from going Neutral (morale boost, greater soldiering ability vs non-neutral alignments, instant-terraform) make them a much more capable race.

I often set the Korx up as Neutral in the Edit Opponent screen as it really seems to make them more of a player in my games.

I wish we had more ways to 'trade' with others, be it renting them a starship construction planet or going halves on the rent for certain starbases.

In fact that gives me an idea! new post time!

Well of course I start wars as Korx I generally pick my opponents already at the start and don´t establish traderoutes to them so that I do not loose investments. But I couldn´t imagine to play Korx without traderoutes. Then I guess it is legitimate to play them neutral from a roleplay point of view as well as strategically. 

As for the traderoutes: There is not only the aspect of money but also the diplomatic. Someone who earns good money from you wouldn´t attack you so eagerly.