Most vocal tracks benefit from a little stereo widening. Very cool trick is to use "split harmonizer" effect in your aux. This technique is very well known and widely used. Originally it was done using a pair of split Eventide H910 Harmonizers and later Eventide H3000's preset "Voc Doubler" (#423). It can be done easily in the DAW world. All you need is a stereo harmonizer plugin. Here's a short list of plugins that can emulate the effect:
The top end roll-off is helping the effect to blend better with the source and emulates the lower bandwidth of the old Eventide H910 unit. Split Harmonizer effect works well with many different sources like vocals, guitars, synthesizers etc. It can make your mono sources wider and stereo sources thicker. Just don't overuse it.
