I do not buy bicycles with the intention of flipping them. I have sold or given away a few but when I bought them it was to keep. But somethings do not stick, others do. But, I do not worry about the money so much, try to keep it reasonable but I have a lot of money in my wheels sets on my wife and my Sports. I just spent near $300 on new Mavic wheels and hub rebuilds for a nice old Bridgestone MTB that is so nice from five feet it looks new, heck from one foot! If I were to buy anything like any of these bikes today they would be hundreds and would be machine built instead of essentially hand built. My Sports looks new and my wife's will be getting there with a little more detail work. Why not spend money on them if the intent is to use them and enjoy them, something that cannot be bought.
I like things that are unique or have personality or show something of human touch and imagination even if machine built. That Schwinn up a few posts with the art deco bullet top forks, very nice and attractive. Just do not often see that kind of work these days.
In the Jeep CJ/YJ/TJ off road world there is a saying, "Built Not Bought" and I think that can apply to many of these bikes, particularly E3Ss. I am not especially fascinated with patina though, I prefer things to look like I just bought them, albeit 20 or 30 or 40 years ago
. And took care of them all along.