Finally, getting to the point, I am wondering what success other users have
  had with building large packages, meta or otherwise from current pkgsrc.  If
  nobody has ever built GNOME for SPARC (I find this hard to believe), have
  other multi-package builds such as KDE, SUSE, XORG, or edesktop been
  successfully built?  It's entirely possible that I'm doing something wrong,
  although I have spent a lot of time reading the pkgsrc documentation, as
  well as man-pages for the various built-in package tools as well as a number
  of the pkgtools add-ons.

I have recently built a lot of things, including gnome, mozilla,
firefox, gaim, via pkgtools/pkg_comp and pkgtools/pkg_chk, on
2.0/i386.  I had very minor problems with a few packages, and it
mostly ran unattended.

That said, I haven't tried to build recent gnome on sparc, but I have
built some of it, and galeon.

  dependency, at some point in the overall meta-pkgs/gnome build process,
  gcc-2.95.3nb5 was installed which seemed to have broken the toolchain).

That's really broken; 2.0 has 3.3.3.  An ultrasparc shows:

Using built-in specs.
Configured with: /home/nick/work/netbsd/src/tools/gcc/../../gnu/dist/gcc/configure --enable-long-long --disable-multilib --enable-threads --disable-symvers --build=i386-unknown-netbsdelf --host=sparc64--netbsd --target=sparc64--netbsd
Thread model: posix
gcc version 3.3.3 (NetBSD nb3 20040520)

I suspect if you figure out why and remove 2.95 (and recursively all
things compiled with it), and fix the problem that required 2.95,
you'll at least be slightly better off.

Try pkg_comp.  I find that having a working system (with packages)
while starting from a clean chroot removes a lot of the variables.

-- 
        Greg Troxel <gdt@ir.bbn.com>