(EDIT: I edited this post after experimenting with wide unison settings and the Unison Balance pane.)

1. I may not be thinking correctly, but shouldn't a high setting for a unison detune make the notes decay faster, given the absence of coupling? (Now, even with an absurd setting such as +1000 for a set of unisons, the unisons beat rapidly, but decay slowly. Of course, one can correct this with the Impedance setting for the note, but it's strange to hear the long, precisely beating unisons when editing in the Unison pane.)

Well, it should indeed because of the reason you mention, and it does. Take for example middle C of the D4 played at velocity 84; with normal tuning, the sound lasts more or less 18 seconds, whereas with unison width = 20 it lasts only 9 seconds.

When the Unison width is 1, the initial decay is fast (direct sound) while the second part of the sound (after sound) has a much slower decay. The decay rate of the detuned unison lies somewhere between those two decays, and does not vary with time.

(note that the maximum value for Unison width is 20, I wonder where you got the 1000 from.)

1. I may not be thinking correctly, but shouldn't a high setting for a unison detune make the notes decay faster, given the absence of coupling? (Now, even with an absurd setting such as +1000 for a set of unisons, the unisons beat rapidly, but decay slowly. Of course, one can correct this with the Impedance setting for the note, but it's strange to hear the long, precisely beating unisons when editing in the Unison pane.)

2. In the model, there appears to be a oddity when the detuning is wide. I'm not sure that there is a limit to the amount of detuning, but you must use the Unison Balance NE pane to hear extreme changes, and then the note sounds thin, like a rattle. When one unison is far off pitch, should there be beating? Instead, won't the unison sound as a separate, distinct pitch? I've heard a piano with a unison that was so badly off in the tenor that I thought the hammer was hitting two sets of unison strings at once. Why would anyone want this extreme detuning? Well, to create a very badly maintained piano, at least one in which the unisons were more off than they can now be set.