I don't know if every move Goodell makes being compared to Spygate is fair or very productive. He handled Spygate poorly and went way overboard with the punishiment, but it is over. I am guessing that if Goodell had to do it over again, he would have handled it much differently.
Fact of the matter is unless either Childress or Favre admits to talking about Favre playing with the Vikes, tampering is hard to prove even with the phone records. There is no NFL rule preventing Favre from talking to Childress especially after he retired, they just cannot talk about Favre playing in Minnesotta. In the San Fran/Briggs case, there were supposably e-mail correspondence that got them in trouble.
I am sure that the Vikings did tamper with Favre. I don't think there is any definitive way to prove it even with the phone records. Why get all upset about it?