Hi Nick, currently the Merge command only merges split up edges into longer edges - in the future I want to have some way to do that to regular curves yet but I've been thinking about possibly modifying the Join command to have that functionality.

Currently the main way to merge smooth meeting curve segments into longer segments is to use the Rebuild command:
http://moi3d.com/3.0/docs/moi_command_reference10.htm#rebuild

- Michael