Well sometimes the choice is pretty easy. If its all rusted, if its not restored its trash. Other times its easy in the other direction. The bike really doesn't have anything wrong with it. Maybe a few minor scratches, but all it may need is the usual maintenance stuff. Tires, brakes, and a good cleaning, but the bike was fully functional and could be pleasantly ridden just as it was.
It's that middle ground that is the issue. It has enough in the way of scratches that sooner or later rust or corrosion is definitely going to be a problem. Like old cars they are only original once, but at some point unless they are restored they can not be enjoyed.
I am curious at what factors other use to make that decision. Also be interested to know where you find things like stickers, emblems and decals for bikes to take them back to as close to original as possible.
Now that doesn't mean I am not going to do something wacky once in a while. I'm about to do that as soon as the shop is done. Anyone else remember the old pedal car known as the Scat car?? Think AMF built it. I had a blast with on at my cousins and I am about to try to build one for a friend of mine's 6 year old. Yet for the most part an old bike should stay an old bike and not have flames unless it came with them from the box.