It is apparently not possible simply to copy the folder and expect the other machine to have access to it, but it is possible to take the contents and transfer them in ad hoc fashion. I fear "permissions" troubles at some point in the future because of doing this, but there's no obvious alternative. Problems — or questions about what to do, for sure — come up also in dealing with the inherent complexities of the filing system in something like the iLife apps.
The Migration Assistant definitely does not work, but it seems to me to be quite objectionably coercive for the Migration Assistant to work only for upgrades (thus channeling the user, cattle-to-the-slaughter-like in only one direction and that to someone else's benefit), and not for even minimal downgrades.