Zimm,
Here is my $.02 Cents:
I don't "Rest" Ribs. Resting is very important in some cooking methods such as roasting. A prime rib will benefit from sitting for 30 minutes to an hour after cooking. The heat from roasting forces the juices inward, and resting allows the moisture to redistribute in the cell structure.
Resting a brisket allows it to stay within the temperature range where collagen breaks down contributing to tenderness.
IMO - Spareribs benefit from 20 minutes of resting uncovered at room temperature to make them easier to slice.
The Amerique hold mode is set to 140 degrees because that is the minimum hold temp to stay off bacterial growth (40 degrees to 140 degrees is the danger zone).
I have an Amerique as well, please try this technique: Rub Spareribs, turn smoker to 250 degrees for 6 hours with a few pieces of hickory. Start checking Ribs at 4 hours to see how they are doing, St Louis cut takes about 5 hours, 5-6 lb Full Spares can take 6 - 7 hours. When you can tear in the middle, pull and let rest at room temp for 20 minutes, slice and enjoy!
Works for me, although there are a thousand ways to do it!
Have fun, eat well!
David