I have had two instances where I had to make a claim on the trip insurance and it out worked fine. I do not believe rates increase if you use it. It is a set rate for everyone. You do have to jump through certain loops.
What happened is that I booked airline tickets on my card for 3 couples to go to Hawaii. About a month before we were scheduled to leave one of the guys developed blood clots, had a minor stroke and was hospitalized for a few weeks. They could not dissolve all the clots and they could not operate because of his weakened condition. Because I had booked the tickets on my card I had to initiate the claim, which I did.
The Airline supervisor I talked to was very nice. The problem was it was Continental who had a defined policy but they where merging with United who did not. Not that the airline policy affected the insurance which we had purchased. The person who cancelled had to get a letter from his doctor and maybe some other documentation and eventually I was sent a check. With some airlines you can get a full or partial refund without insurance but it depends on their policy. The long and short of it is that the insurance worked fine in this case.
Another time the same couple was on a cruise with us when she had what I would call a minor ailment. She had a small amount of red blood from a hemorrhoid. I advised them against going to the doctor on board but she did. He told them they would have to get off the ship and go to the local hospital because if she had a problem at sea he could not or did not want to deal with it. They left the ship went to the hospital which they had to pay cash; spent a few hours there; missed the ship's departure and found us at the next stop. The insurance paid for everything. Medical, hotel, and a flight to the next Island.
I'm now trying to find an excuse not to book them with us on an up coming trip to Alaska.