Idealizing subjectivism: X is intrinsically valuable, relative to an agent A, if and only if, and because, A would have some set of evaluative attitudes towards X, if A had undergone some sort of idealization procedure.
I feel you’ve been discussing how confusing the consequences of the definition above are. Then, why don’t you just drop the definition and revise it?
I would propose: X is intrinsically valuable, relative to an agent A belonging to a close-influence set of agents S, if and only if, and because, A and all the agents in S would have some set of evaluative attitudes toward X, if A and all agents in S had undergone some sort of idealization procedure.
And by close-influence set, I mean a set of agent that cannot be influenced by anything else outside the set.
I think that most of the concerns you are describing come from assuming that the idealisation process is personal and that there are multiple idealised evaluative attitudes toward something.
When you assume one unique evaluation, you can view that the agents are all trying to discover it. In the end of the process, there are no further questions, everybody agrees, and subjective is the same as objective. During the process, you have differences, personal evaluation, change of hearts, and all the chaos you describe.
Resources and time are probably limited to carry out the idealised process on every possible object X, but hopefully as a human race we can discover unanimous agreement on one or two big important questions within the next few millions of years.
Let me build a story-case for unanimous convergence.
Imagine you are troglodyte, and you are trying to assess how far the hunting ground is. You need to estimate where you are, and what time of the day is, because being at the wrong place at the wrong time means either meeting a stronger predator or missing your target. Now, how do you evaluate the way you measure time? Do you have a preference for looking at the sun, perhaps it is a cloudy day, is it a good idea? Do you prefer to listen to your human body rhythm (when you are hungry)? Do you follow somebody example? Do you look at the rain? Do you watch the behaviour of the animals around you? Do you draw symbol on the ground to recall your way? Do you break tree branches? Do you leave a trail of stones? Do you dig a road?
The troglodyte is probably going to be in dilemma and debate the issue strongly with his clan-mates (like it happens to the agents in many of the scenarios you discuss about). Nowadays how we measure time and map location in our everyday life is something we mostly all agree.