I definitely agree that the greater context has an influence over the tense and aspect used in the main clause. But I'm not convinced the subordinate clause has no influence.
I am going to have to come down on the side of context over tense/aspect. We write and speak to convey meaning, and we choose tenses so that we can convey the meaning we intend.
There is a certain truth to your feeling that a subordinate clause influences the tense of a main clause, but it not an influence created by a grammatical relationship. Rather, it is created by a semantic relationship between clauses. Take the following sentence as an example:
If I were not afraid of losing my job, I would tell by boss how I feel about his new policy.
Grammatically, the conditional is required in the main clause because the subordinate clause is subjunctive (expressing a counterfactual condition). However, the context of the situation (that is, the fact that I am
afraid of losing my job, creates the need for the subjunctive as well as the conditional in the main clause. If I were not afraid of losing my job, the context would be different, and—as a result—so would the grammar.
If the sentence regarding getting up and eating breakfast, there are several choices you could make regarding tense, and the choices should be made because of context, not grammar. Consider the following:
Before I left for school, I ate a big breakfast.
In this sentence, there is at least a chance that there is no significant relationship between going to school and eating breakfast. It could simply describe the order of two events.
Before I left for school, I had eaten a big breakfast.
Here, there is at least a hint that the big breakfast will have an effect on what happens after I arrive at school. If this is indeed the case, then had eaten
is a better choice—not because of the grammatical relationship between the two clauses, but because had eaten
suggests a more meaningful relationship between two actions.
In short, meaning is everything, and the right tenses help convey precisely what is intended.