There are a lot of things going on in the original poster's relationship with his wife. According to his description, the spanking he described was an important step in resolving their problems. I believe him.
Marriages need constant work. Nothing, including spanking, is a one time solution after which the couple can stop working on the marriage. However, it does sound like this spanking was a turning point for them and their relationship is moving in a better direction now.
I am pleased to see the original poster feeling more hopeful about his marriage and it disturbs me to see you dumping on him with a "it probably won't last" attitude. It seems to me needlessly cruel.