Two separate, but perhaps related questions, with my answers:
1. How long do you expect to keep your current boat? Why?
2. Can you anticipate how long your boat might last? Perhaps based on when would the cost of maintenance/upgrading be more than the boat is worth - or maybe the boat just starts to fall apart.
For my Bristol 45.5
1. Probably be looking to sell when we complete our circumnavigation. We intend to return to Lake Ontario and the boat is just too large for most of the little harbors we would be visiting. We have terrific reciprocal visiting privileges between yacht clubs, but most don't have docks for a 45'. This assumes we can get a decent price for the boat which may be a big assumption for a few years.
2. I think she will be going strong for many decades - the quality and strength of construction is so good that boat value is high enough to justify major upgrades like a new engine (not that is needed any time soon). I assume we will need new #2 and main on our return since we will likely be 40,000+ miles on genoa and more on the main.