I always tell be people to do what they enjoy most. That is, after all, why you are playing the game. However, you do have to take into account that you will be grouping with others, and in these cases the experience is shared. It will be important to them and you that you have secured the abilities that will be useful for group play. In the lower levels, I'm guessing it isn't as important, but it will become more so as you progress.

Personally, I'd go crazy seeing those 'additional traits' slots empty as I got closer to 30 when those secondary traits will only make my character stronger and have more utility available if I level several classes. That's what makes the game fun for me, but it might be different for someone else.