I'll buy a drink for the first FTer who books their, say, BOS-WIL Acela ride as BOS-NYP-WIL using the multi-city option (which will get you a through fare, though the higher fare bucket prevails) and attempts to upgrade the BOS-NYP segment with a coupon.
If you've an hour or two to spare, note that you get the 500/750 point minimum for BOS-NYP, plus the pro-rated value for NYP-WIL, plus a visit to your favorite NYC eatery.