As suggested by Joshua Bloch in Effective Java, it's not a good idea to derive a value associated with an enum from its ordinal, because changes to the ordering of the enum values might break the logic you encoded.
The second approach you mention follows exactly what the author proposes, which is storing the value in a separate field.
I would say that the alternative you suggested is definitely better because it is more extendable and maintainable, as you are decoupling the ordering of the enum values and the notion of hierarchy.
