The problem is that the law is pretty vague, which gives the FAA flexibility to interpret it in different ways and still technically be correct. That might even be by design. If the law were too specific, it could make enforcement a lot harder.
For example, regarding the
sailboat inspection scenario,
@Vic Moss mentioned
here that the FAA previously held that such flights were categorically non-recreational. So, did their definition of "recreational flight" change, or are they just choosing not to enforce the law for certain non-recreational flights?
I believe it's the latter, but one could easily argue it's the former. And that’s basically what's being debated in this thread.
And while it's fun to speculate and debate, what really matters is how the FAA will interpret your specific situation. So, if you're planning a flight that you can't confidently say is for personal enjoyment (like "I'm flying to inspect my roof for damage"), it's a good idea to check with the FAA to get their current stance.