My dad was a new car salesman back in the day.  I remember him telling me that he once lost a sale because the customer didn't want holes drilled in their new car for a dealer emblem.  Before the sale, my dad had instructed the new car prep guys to not install the dealer emblem but for some reason the instruction was lost somewhere in the process or somebody was on auto-pilot, so it got drilled.  The customer was put off by the whole thing and went elsewhere.

It's true, though, they were considered worthless back in the day but now they give some credence to the car's lineage or history so they have become a valued commodity.

The high school sticker is understandable - back then you would not have considered it important but as time passes you realize it was part of your personal history with the car.  It's unusual for anybody to be able to keep a car that long so it's significant in itself.

BTW, do you have any photos of the sticker?  You might be able to get one made up if you did...