I had this conversation with an old buddy of mine just a few weeks ago, driving down to philly to pickup a 1950s west german record player setup.
He and I have always had older vehicles, always worked on them together. My first car was a 1982 crown vic, his was a 1984 lincoln towncar. Learned from each other how to fix stuff, although hes more into it than I am, he has a mechanic shop at his house, I just work on my own vehicles.
I enjoy my IDI for all the reasons already mentioned and because I have the time and skill and shop and tools to fix everything on it myself. If I had to pay a shop to fix it due to any 1 of these factors, then it would not be worth owning. It works for me because I dont NEED it to work all the time, every day, everytime I need it. If I go to harvest some firewood and find it's rear brake line blew, oh well, no big deal. Spend some time replacing the line instead of getting firewood. However, if I hop in to respond to a fire or a search and rescue event, or any other critical work related event, blowing a brake line (for example) means huge consequences and there is no room for that for some people.
Thats where a newer truck makes sense and an older truck does not.