Have a logic board issue -- worth it to replace?

I have an iMac G5, about 4.5-5 years old now. It frequently shuts off and often refuses to turn on. After completing a series of troubleshooting guides at the apple website, it appears I have a faulty logic board.
According to the people at the Mac store, a replacement logic board should be
$879.95 plus labor.

I am assuming it is not worth it to replace the logic board (right?), but is there something else I could do to at least stave off the effects of the failing logic board? Or, is there some other alternative I have not yet discovered?

Thanks.

 

Ok. Thanks.

EDIT: By the way, will the logic board issues get progressively worse, or is the present shutting off/turning on issues pretty much the worst of it (barring other different failures)?

 

I am backing all my stuff up now.

Thanks for the input guys.