Actually, a 5-1-1 mix will promote much faster draining soil which will allow it to dry out quicker than normal potting soil. By having a 3-1-1 mix, you will likely retain a lot more moisture than you would with a 5-1-1 mix. I dont know of any concerns with pine bark in introducing pests any more than any other component.

I reused my 5-1-1 from last year and actually added a little more potting mix to it for this season making it closer to a 3-1-1 or 4-1-1 mix in hopes that it would retain a little more moisture and it does. The more bark, the more "airy" your mix will be.
Bruce

Probably in cooler Heat Zones (like mine, like yours) mulching is not really necessary. But I do it with mini nuggets. That help to keep the soil undisturbed and reduce watering needs. But I think it can help a great deal in warmer climates.