I don't think your benefit example is too much a problem in practice, we already have the access setup for that (ie its the same one for you).

For the other example, I think a nice compromise is to have the AI be able to do things only with your express permission. In your example it finds flights that it thinks are appropriate, sends you a notification with the list and you can then press a simple yes/no/more information button. It would still save you a ton of money, but it would be substantially less likely to do something dangerous/damaging.