I have been lucky enough to acquire mostly nice condition kettles. Personally, I just go for what I want no matter what the condition. To Me, it is all about rescuing and enjoy using them knowing the history of these kettles. We don't get much rare kettles here but anything interesting in any condition is ok by me.
I love seeing these cool kettles pop up ( latest example- MLH Glen blue for $5 score by one of the member). Not often for these kettles but we all see them come up for sale cheap or for free all the time. In most all cases, any cool vintage kettles can be had for reasonable $.
It is unrealistic to rate kettles and see no point in doing so, but when that day comes and greed sets in with really high asking prices.... I am out.
Just remember, outside of us kettle heads.... no one is interested in these kettles no matter how special....until they find out they can charge lot more because we kettle head said so. We can't stop this from happening but at same time no need to promote driving the prices up.
To me, anything with logo is out.... for some, they only collect logo kettle. I love Cado kettles, some of you hate avocado colors. There is no way to quantify and rate kettles. Even if you can... why would you.