But my real question about backing is whether or not Lacy's Stiff Stuff is
worth ordering, since I can't find it locally and since it seems to be so
highly recommended in most sets of directions I've read.

No. Because -- 1) too expensive, and 2) Pellon interfacing is basically the
same.
~~
Sooz
-------
"Those in the cheaper seats clap. The rest of you rattle your jewelry." John
Lennon (1940 - 1980) Royal Varieties Performance
~ Dr. Sooz's Bead Links
http://airandearth.netfirms.com/soozlinkslist.html