In the situations above, the people will be created and, happy or not, eliminated as soon as they are no longer needed.

I don't mean that they'll exist permanently. It's good for a happy person to exist, even if it's only for a little while.

Also, I think it's not obvious whether we should create more happy people, or just improve the lives of the currently existing people.

You shouldn't go out of your way to avoid running programs that create happy people. More generally, if it would be helpful to run such a program, but not quite worth the resources on its own, it may be worth while if it's a happy person. That will happen about as often as a program being worth while on its own, but not worth running because it creates a sad person.