Pretty much the only exception to that rule for me is when the computer is an observed collectable: The price for resale exceeds the value of the computer based on it's capabilities. But at that point the computer stops being a tool and becomes a collector's item. My TAM is a case in point. The 5500/250 has equal capabilities, and paying more than $50 for one is certifiable insanity (IMO), but I happily paid several hundred for my TAM. I won't cannibalize the TAM because it is not a tool. It is a collector's item that I invested in.
The Color Classic is similarly collectable but holds significantly less value than the TAM. As it is less valuable, I had no problem gutting and carving mine to convert it to a Takky (though the conversion is as yet incomplete). The 5x0 series and 5xxx series have no collector's value and thus no intrinsic worth other than what use I can get out of them as a tool. That doesn't stop me from buying one and preserving it in my collection, but I feel no guilt about destroying a second, third, or thirtieth for any reason provided that the destruction results in some increase in overall net worth or even some temporary entertainment (though, actually, destroying one for fun might make me feel guilty because I have deprived someone else of a useful tool just for entertainment's sake).
Peace,
Drew