Is it worth my time to replace a water pump on a 1997 Honda Passport?

If it's working and not leaking, probably not. If you're having a good deal of work done on your engine (or especially on your cooling system) anyway, it might make sense to replace an elderly but still working water pump at the same time; the part itself is typically pretty cheap, and most of the labor is in getting to it, so if they've already pulled the engine out to replace the radiator replacing the pump as well is only an extra 5-10 minutes of work.

If your water pump isn't working, replacing it is certainly going to be cheaper than buying a new car. On most cars they're simple enough to replace that anyone of even moderate mechanical aptitude should be able to do it with the help of a repair manual for your car (about $15) and the pumps themselves tend to be in the $30-80 range for most cars.

I have replaced water pumps myself and I am not a skilled auto mechanic by any stretch of the imagination. My experience is that in most cases the hard part is figuring out how to GET to the piece that needs replacement; this is where the repair manual really comes in handy, because on my car it suggested removing the front passenger side tire and wheel well cover, which never would have occurred to me (seriously, I assumed it was part of the body, or at least riveted on ... like I said, NOT a mechanic) but as soon as I did it the pump was right there and (relatively) easy to reach.