If I may quote The Matrix Reloaded for a moment: "It is
purpose that connects us, that pulls us, that guides us. It is purpose
that defines us."
Purpose is one of the larger struggles in bringing old dinosaurs
back into operation. Most people lack purpose for these old 'puters.
The trick is finding something for them to mull over or do nothing at
all (I'll explain the latter later on).
Extending the life of an old machine can sometimes require the user
to jump through certain hoops during preparation. As I outlined in
Calculating the
Usefulness Equation, there is an easy way to figure out a machine's
destiny.
( Final Power / Cost of Preparation ) ≤ Final
Usefulness
As far as Old
World Macs (pre-G3 models) go, I highly recommend hot rodding,
which does add to the cost of preparation for use. There are G3 and G4
upgrades for almost every PCI Power Mac in existence, not to mention
'040 upgrades for 68030 models.
My favorite task to allocate to an older machine is running a tiny
version of Linux along with a web server. It's the ultimate proof of
concept for repurposing a machine. It proves that the machine can still
be used in this day and age.
There is also a great purpose for Old World Macs that have ethernet
and LocalTalk: a LocalTalk bridge
for your non-ethernet Macs. This is a particular purpose that can be
run in the background on more powerful Macs, or in the foreground on
not-so-powerful ones.
You should avoid any Old World Mac that will cost more to get
running then it's final product will be worth. If you're spending $400
to get a 40 MHz Mac IIfx machine
in running condition, you had better have a good reason.
For example, hot rodding my Power Mac 8600 only cost me $125.
It's running a 400 MHz G3 upgrade ($20), 512 MB of RAM ($25), dual 10
GB SCSI drives ($50), and the computer itself cost $20 at a garage
sale. It is a great web server (not to mention almost full featured)
and mention a powerful OS 9 machine. The equation is definitely
balanced.
This brings me
to my next point: The exception to the Cost to Purpose calculation is
Mac museums and collections. In the Old World category, there are many
rare and awesome machines that may not have any true power behind them,
but they look great on display because of their rarity or interesting
design. The Twentieth
Anniversary Mac and Macintosh
TV are good examples.
My personal preference when searching for Old World project
computers is to focus on expandability. The more I can put into it to
improve function, the happier I will be with the finished product. This
will vary from person to person, depending on the final goal of the
project.
My best advice: if you see a dump-bound Mac, take a gander inside
and give it another chance. You might just be surprised.
Next time we'll visit hardware and upgrade compatibility concepts
you should keep in mind. 
