Now that is a toughie. While you may not have the Core himes for dark/fire, you do have the second best choises at hand. If you are willing to drop some money for a miracle ticket for either dark or fire, you can build a strong team without rerolling.
If you don't want to spend any.... i am not sure. Really. i would not reroll cause of re-leveling, really don't like it.

But please get some more opinions, since you are imo in a delicate spot.