We don't have the identity and value overlap with others that we'd have with copies. The contract would just be formalizing it. I think it's a silly way of formalizing it. I respect my copies' right to drift differently than I do, and will then cease cooperating as absolutely. I certainly don't want to lose all of my assets in this case!

This is a good point - one could already sign a future-altruism-contract with someone, and it would already be an expected gain if it worked. But we only see approximations to this, like insurance or marriage. So unless my copies are enough more trustworthy and thoughtful of me to make this work, maybe something on the more efficacious self-modification end of the spectrum is actually necessary.