The idea is not completely worked out. But the basic idea is that I distinguish between statements used as assertions and statements used as assumptions. (The division of statements into beliefs and preferences is orthogonal.)

When a statement is used as an assertion, the meaning of the statement flows from the relationship between the statement and the actual world. The truth of an assertion depends upon evidence. An assertion "pays the rent in anticipated experience".

When a statement is used as an assumption, the meaning of the statement flows from the way that the assumption changes the way the world is talked about. The presence or absence of an assumption changes the meaning of statements - it may even change a statement from meaningless to meaningful. An assumption "pays the rent" by providing new ways of thinking about the world.

As I understand it, when we choose MWI over Copenhagen, we are making an assumption, not stating an assertion which may (depending on the evidence) be true or false about the world.

So, given this framework, I claim that the question of whether beliefs must be distinguished from preferences is not something to be decided by evidence or reasoning. Instead, we make that distinction as an assumption. Having made that assumption, we can then go on to make assertions or form analogies that flow from this assumption. The assumption enables speaking and reasoning. And we can make the "meta-assertion" that the distinction itself should be classified as an assumption.