I will be interested to see what others say but i'm pretty sure that most long term tourers don't bother with it. Its not a bad idea to have some insurance in the early days since its the early days when you are developing your touring skills that you are most vulnerable but that's just an opinion.
Cycle touring would not be considered needless danger. Needless danger would be like riding into a war zone, or base jumping. But if you have a policy that has that clause you might want to run your itinerary by them before setting out. Get any clarification in writing.
Another way you might look at it is if you have a really good credit card. Some of these provide you with autmatic travel insurance if you buy a plane ticket with them. Mine does but i have to admit that i never get to see the policy so I wouldn't know what it covers and what it doesn't or for how long. So whenever you think you are covered do explicitly ask them about what things you may do eg bicycle touring to xyz place and so on.
But you can minimise your safety risks by many other non insurances means. eg vaccinations. That would be my number 1 recommendation. Including rabies shots if you are going in countries where this disease is prevalent or where there are vicious dogs.
Ride on small country roads as much as possible avoiding busy highways.
Lock your bike up at nights inside a hotel or off the street.
Ride carefully always.
have good strategies for the security of yoruself and your gear. Learn how to protect your belongings.
In some countries if you are camping, its genearlly a good idea not to broadcast your intentions and to camp out of sight.
Things like this.
Be suspicious of people who come up to you and offer hospitality to readily, especially say in a place like india for example.
