The idea is to remain as objective as possible, and not be swayed by the sentimental attachment.
The issue is that owners DO become attached, they DO spend more money (over-capitalize) and they almost invariably DO have a false impression of the vehicles real value - because they have spent hand-over-fist trying to keep it alive.
The original point isn't lost on anyone, it's just a simple case of justifying why money was spent.
The underlying reason remains the same - we all have developed a semi-symbiotic relationship - which is to say the parasitic portion (aka money) is justified by the return (reliability, use, enjoyment) on the injection of funds.
And that is why the question in the OP remains relevant..... :D

