The main thing that will kill all equipment is the capacitors. They will only last about 25 years (less if you use them a lot). And when they go bad, they cause other things to fry. Replace all the electrolitic caps in your unit (and it's power supply) and run those things past your retirement age. 
(All warrantees are off if you get an unprotected power surge the house though)
Plaz
I got a ZX81, ZX Spectrum and C64 that all scoff at your 25yo capacitor limit. Average of 30YO and counting.....
Agree capacitors are the soft point over all the other components...
It's a pity she wont live forever, but then again who does?
You should be wary of experts that advise how long things will last. I remember the line that cassettes and computer tapes will only last 5-7 years maximum. 30 years later, still loading fine.
I heard that 2000 years ago Roman jewellery experts used to say that bronze broaches would only last 100years max. I don't suggest you bury your A1200 in a peat bog though....
