Yes: The distinction I see between stars and A/B (in the "doing order" sense) is just the timeframe. In both cases they are tentative, but with just a few starred actions, intended to be finished in a few hours, it is acceptable to perhaps change the order and even unstar them. But to base the whole Next list on this kind of classification .... No, not meaningful. You would have to change it all the time.
Yes: Ideally, but I do not know how, when selecting tasks to do, the perfect solution would be to narrow down the choice mechanically (filters etc) to a manageable number, and then make the final choice using your "gut" (common sense, balanced assessment of the four factors etc), and to do that, just as you say, you would have to consider the difference in priority (importance), the "cost" of switching contexts X/Y, the "loss" incurred by having a slightly wrong energy type, etc.
All of this is something you do quite easily using your "gut" once you have narrowed it down sufficiently and do not have too many options left. The main problem (with the apps I have seen so far) is to narrow down the choice.
I believe one healthy step forward would be if apps offered the filtering options to quickly not just "show tasks with this tag" but also had the capability to exclude tasks with a certain tag, and to include. By successively using such simple filters (e.g. alt-click the tag, shift-click the tag etc) I believe you could narrow down your choices quite a bit without excluding true candidate actions. I am not sure how much you could narrow it down, though, because I have never seen an app that has this. And then the user would also need to define a solid set of tags for his/her personality and situation in order for there to be anything to filter by. But it seems like a simple enough feature to implement, so I really wish some developers would offer this, so that we could try.