Oh, yes indeed, this sort of thing is still useful, especially if you don't have
any other equipment. You can start with the old Macs and the old software and
build upon your successes. I still introduce one of my classes to Macpaint, and
I like to use Macdraw for a couple of units because it requires students to make
their own colors by checkerboarding the primary colors in the pattern editor....
Eventually, we move on to higher-end software, but practicing with many programs
pays off through student perceptions of what is really "common" in the common
user interface - and what is not. Mastering only one application does not bring
about the flexibility with the interface that will carry students into the next
century, and old applications are fine for creating such flexibility! Besides,
the images are still sophisticated, and that is really what counts - using the
computer as a practical tool, not as an end in itself.
Keep the old equipment and go for it!