I can't see George Bush being welcome to speak anywhere outside of a few oil companies in Texas. Republicans will disown him for destroying the party. The Christian right will have nothing to do with him because he had a chance to stack the court with right-wing nutjobs and failed. I can easily see Bush hitting the bottle hard and dying of a failed liver within 5 years of the end of his presidency (be it through impeachment or natural causes).

However, I could see gay groups inviting him to speak for nominating the first homosexual Supreme Court justice.