I accept your definition of
perfect as one that applies to my God, but I disagree that it precludes desire. You define it as
Which is so good that nothing of the kind could be better
The question is of what kind is God? Anything with multiple traits can of course be classified in multiple ways. We could say God is of the kind
creators of universe(s), but since He is the only one of that kind, He would be perfect by definition. This is too narrow. I submit that the correct kind to place God within for the purpose of your definition is
intelligent agent, that is a being possessing power of discernment and an ability to act.
In this case, God is the intelligent agent that no other intelligent agent can be better than (or, I might add, as good as). If God is an agent and actor, and desire is a precondition of conscious action, then the state of being the perfect agent cannot be a state which precludes desire. It would only mean that God's desires are better desires than any others', perfect desires, in fact.
Furthermore, it is not at all clear that your definition precludes improvement itself. It could be taken to mean that a perfect thing is always the best of its kind at any particular moment, but it is not necessarily so that its
kind should include future instances of itself. In other words, there is no greater being than God now, five minutes ago there was no better being than God, but in those five minutes, God may have made
himself better.