For the most part, the more you use them, the more they will produce. Basil and parsley are great examples of this principle. When you don't pinch your herbs often enough, they tend to go to seed or become bitter. Water soluble fertilizers such as Miracle Gro are easy to apply and readily used by the plants. If you prefer to use something organic on edibles, try one of the dry natural fertilizers formulated for flowers and vegetables.
Many herbs are absolutely beautiful plants.
There is nothing wrong with growing them for just that reason. Some of the herbs now classified as ornamental were originally used medicinally. There are hundreds of recipes for using herbs as medicine, and they have been used for that purpose for centuries. But we advise caution. Recent research has found that many herbs have side effects that we were not aware of before, some of them dangerous.