I bought my G4 summer of 2001 and am still using it ( 3/7/17) for desktop publishing, currently building a twice monthly community newspaper averaging 40 color pages. So, yes, vintage G4s are worth maintaining.
Today, a nearby lightning strike took out my power supply and I was able to replace it using the instructions on this site. (Plus, I have a spare G4 I borrowed from!)
I plan on using this G4 until it melts!