I also wonder what kind of work a CRI might get
I suspect most CRIs get the qualification for personal satisfaction and to help out their group or club. I doubt very much if there is a living to be made from.
As things stand you need the full CPL to be paid for instructing, but only the CPL or ATPL exams for the FI rating.
The actual aircraft is somewhat different as well... wouldn't you say
Just a bit. It is unlikely to meet Rod1's original criteria for cheap flying into his dotage. I had a few hours on an Christen Eagle a few years back but due to very sad circumstances never got to the point of being solo. However, my impression is that such aircraft - including I suspect the likes of the Pitts S1 -are a handful. I know there are those who would challenge this and claim that their vices are over done, but that is my personal impression arising from a grand total of about seven hours in one. Of course in the hands of an experienced pilot like Stik they are magnificent and maybe today being a bit older and hopefully a little more developed in my skills an Eagle would not seem such a challenge. There is still a part of me that would like to lay a ghost in that respect!
Again, even with the money perhaps not the sort of aircraft to be thinking about owning in the last twenty years of your active flying.