The reason for the complexity in my example was to make it relevant to the real-world decision of whether we should concentrate our attention and efforts on the singleton scenario or not. Should I have introduced a simple example first, and then the more complex example separately?

But in this format, it looks silly to do anything but treat it as the simple expected-utility problem a la Robin. Is this somehow not a correct version of your dilemma, or is there some reason we should be horrified at the result of choosing A?

Not exactly horrified, but it's not quite intuitive either, especially if you make the numbers more extreme, like in my example.