Hi shannon,
Nice article, thanks as usual. I only skimmed it, but one thing to consider:
Combis have a very important advantage for live jamming (of the sort where you are actually doing everything in real-time), especially when using the KARMA function, or when performing real-time sound edits with the RealTime Control Mode of the Control Surface: anything you edit in a Song cannot be reset reliably, or easily. (You can try to use the COMPARE button, but this is flakey for this sort of operation that has nothing to do with actual editing of sequencer data.) Whereas, with a Combi, you just reselect it, and voila - back to the starting point. This can be especially important for rehearsing something over and over. With a song, you either need to reload it from backup, or recopy it from the original combi to get back to the starting point. This may not be a problem with a set list where you're moving in a linear fashion…