Kyle wrote:
In the bath, we put up one of those double-tier towel racks and, of
course, it's 30" long which means I can only anchor one end in a
stud...the other end had to go into drywall.
(snip)

So my question: any ideas on how to give a solid mounting surface to
this one end of the towel rack that's got bad drywall? Some trick to
insert a piece of 1x3 or such (for screwing the rack's bracket into)
inside the drywall without creating too large a hole to cover?

You could install a 36" 1x4 (oak or whatever matches the cabinets) and
then attach the towel rack to that.

It would cover the damaged drywall and would be plenty strong. (you'd be
able to hit three studs)

If you have time (and tools) you could make the edges look less 1x4ish
with a router or by attaching 3/4" quarter round or similar trim.