I do sometimes think of the lenses I once had, and mostly traded in at a retail shop for something newer. This talk of Steinheil reminds me of a 135mm f/2.8 Auto-D Quinar in Pentax mount that I bought new... focus was always a bit stiff, and control rotation was not consistent with Takumar lenses, but it did feature its own cable-release socket. And I recall an 85mm f/1.8 Auto-Takumar with semi-auto diaphragm that would now be a good match for my new/old model H3, but which was traded for an 85mm Super Tak that I still have.
But in general I tend to hold onto stuff even if I'm not using it, with the idea that I will use it again later. In particular I have never sold ANYthing to raise cash for other pressing expenses like rent, medical expenses, loan payments or car repairs. First, I'm a lousy seller, and I hate to take a big loss for a quick sale. It's inefficient. So I concentrate on being a good buyer. I'm careful not to overextend myself financially on purchases, as it's just not comfortable to run close to the edge of disaster. I carefully consider the financial effect of any purchase, and make sure to have adequate backup resources.
This is a stodgy approach, and I sometimes envy those who choose to flit from one goody to another. They're getting hands-on experience with lots of fun stuff while I'm slogging along being carefully conservative.
(Geez, this is funny: me fiscally conservative, in light of my mother's warning to my bride at our wedding that I was a spendthrift who needed a restraining influence! The other side of that coin is my wife is more of a gadget-hound and spendthrift than I, and could only restrain her humor at my Mom's advice.)
It's actually
cheaper this way, so I can afford to slowly accumulate some fun stuff to enjoy over time. I don't trade my car in for a new one every year or two either; I've had my BMW M3 for over 4 years...