I've never gotten trip insurance, but then the only organized tour I've been on was very short and didn't cost much.
However, I do get travel insurance whenever I go anywhere. Travel insurance covers any health issues I might have as well as making the aspect of dealing with my death (if I should die out there somewhere) easier to deal with for my family. I also have insurance to cover my bicycle in case it happens to get stolen or damaged. That insurance is also useful for crossing the border as proof that I actually own the bicycle.
And just a little story to add to this ... not a cycling tour but ...
A coworker of mine signed up for a package deal through a travel agent to have her wedding somewhere in the Carribean. Everything was all arranged, and the guests were given a special deal on flights, accommodations, etc.. Most had already put down deposits. My coworker just told us today that the transportation has fallen through leaving everyone high and dry ... and leaving the bride and groom scrambling for a new location for their wedding. They are now in the process of trying to get all their deposits back. Here in Canada we do have some organizations who go to bat for people who end up in these situations, so they are making use of those organizations but it could be a very long time before they see their money. They now wish they had taken the insurance.