Our goals when we paint anyones home or business are results the are pleasing to the eye, lasting, and can be maintained with minimal effort.  The better the quality of paint the better these three aspects are achieved.   Better quality products for the exterior have better color retention, this is very important in Florida.  They are more mildew resistent and washable.  The same millage (thickness) of the top product has a greater compaciity for these properties because of the chemical make-up of the product, i.e. quality. You are applying a denser product.  Interior wise, you want a smooth sheen that is easy on the eyes, odor comes into play, washability, and durability.  Again, the quality product will give you the best results.  You will have the lasting color "richness"  you desire.  Our recomemdation: Pay the extra and get the best you can afford! You will be happier with the end results.  Remember your  painting contracter; they will  guide you to make better choices.