Agreed, Andy.
I rebuilt both a Campagnolo ErgoShifter and a Dura-Ace STI shifter this year, replacing a few worn bits on both. Both shifters worked beautifully afterward, but it was by far the most difficult bike-related task I have ever accomplished (never rebuild a Sturmey-Archer though!). The amount of small, thin, delicate parts in each is mind blowing. How they engineered them to work from paper drawings (CAD?) I'll never know. I can see why people toss them when they don't work any longer. Though, if you could get good at rebuilding them, there is absolutely an endless treasure trove of broken stock out there available for next to nothing. So long as you have a stock of NOS replacement parts on hand, you're in business.

But for your first few repairs, be prepared to parse together two or three YouTube videos on how things to back together with proper technique and perfect order. Try not to be frustrated!