If you're getting bonuses to damage on your spells and/or exploiting elemental vulnerabilities, it can be quite good. Targeting touch AC means you're much more likely to hit, after all. However, the 5d6 cap gets worse and worse as you get to higher levels, and with two claws, a bite, and the strength bonus from Dragon Disciple, you're MUCH better off trying to full attack things to pieces when possible. In which case, you'd have been better off buffing yourself with Enlarge Person, Bull's Strength, Haste, etc.
It can be a good tool for approaching and against foes with high DR, but most Dragon Disciples are better off focusing on enhancing themselves and ripping enemies to shreds dragon-style. If you really want a Shocking Grasp-centered build, Magus is by far the best class for you.