Given that experience, I felt that paid for software should
come with sources so that when something goes wrong you can
figure out what happened and may be find a way around it. I
had no problem trying to "use the source" but first they had
to provide it; the real documentation! If in the original
vendor goes out of business or decides to stop supporting a
product you bought, you're not stuck. Just as the original
Tektronix oscilloscopes continue being useful.
Ah herein is an issue. Tektronix (when I worked for them) was suing the US Gov because they had taken the schematics of one of their scopes (the 465 IIRC), and had someone else make a clone (Keithley IIRC). Tek eventually won the case, because the new instance was a duplicate that you touch and feel.
Software gets tricky. Franklin, of course, copied Apple's ROM and Arthur Kahn (lead lawyer for Franklin) that they had published the sources in their manuals and processor so designed to run it as it. They had not copied Apple's chip, they used different devices but they had used the same functions, entries etc. They had changed some things, but they had used the sources that Apple had published as the place to start. He almost won, because the SW did not have a physical instance. In the end, he was able to set the precedent for the idea of the 'clean room' BIOS of the PC. One group writing a specification, but the new code being implemented by a group of people that had no knowledge of the original - only the new specification.
BTW: I understand where you are coming and I too miss those days. Hey, my own first learning in electronics was getting the schematics for a TV or a Radio and troubleshooting them. I also spent a number of hours, staring at Wozinacks Apple-II sources trying to understand what he did.
The problem is that in the world were the replica is no different from the original, it makes IP protection extremely difficult.
As I said, the issue end the end is who gets to say? The originator of the IP or the customer/user of it?