This is a very revealing post. I thought you were well and truely wedded to the modern machinery, including the Rotax. Concern about if the engine fails implies a tighter flying budget in the future. It is interesting that your likely route is an aircraft dating in design from some 60+ years ago. That really raises the interesting question as to whether aircraft have made any progress at all; certainly in terms of affordability they appear not to have. As I understand it something like a D120 or 1050 will tick almost all the boxes: unleaded, economical, reasonable speed (not as fast as an MCR but fast enough), load lifting, reliability and ease of maintenance. The likes of the MCR owner (and other VLAs) face what as the aircraft enters middle age? Much higher cost for an engine rebuild or replacement or for any significant work on their composite structures?
Are you perhaps being unduely pessimistic? Surely like many owners you will build a general engine and airframe fund to deal with these issues as they arise. You don't strike me as falling easily into the group owning mentality!
For myself, who has little time for long touring, I see little reason to move from the current group ownership structure. However, I am very conscious that the very modest £100 per hour for the Chipmunk cannot last. I do need something to allow for more frequent but less costly sorties. The answer would appear to be single seat. The insurance comes down a lot, especially with hull values in many cases being sub £10k. Hangerage is cheaper and operating costs tiny (unless it is a Pitts S1!), as is maintenance. You can even rent them out to someone you really trust.