1. About Mexican officials -- my understanding is that the ambassador did everything right -- unfortunately it cost him his job. Mexican officials were embarrassed, and they rightly should be. Hiding the truth of their situation and brushing it under the rug won't make anything better. The fact that it's in the open now hopefully will motivate.
2. About the government becoming less open -- they are incredibly closed off as it is (to the outside), how would they be any less open? If being more closed internally due to fear of leakage is worth the cost of potential poor communication across agencies and thus raising the risk of poor execution in times of crisis -- then that's a decision they have to make. Truthfully the risk has always been there, Wikileaks' actions don't change anything other than bring awareness to that risk. Personally I don't believe that fear is worth it.