With respect to question (ii) ["What is the role of simplicity principles in different areas of inquiry?"], there is an important distinction to be made between two sorts of simplicity principle. Occam's Razor may be formulated as an epistemic principle: if theory T is simpler than theory T*, then it is rational (other things being equal) to believe T rather than T*. Or it may be formulated as a methodological principle: if T is simpler than T* then it is rational to adopt T as one's working theory for scientific purposes. These two conceptions of Occam's Razor require different sorts of justification in answer to question (iii)[Is there a rational justification for such simplicity principles?].
While this system of classifying ways of formulating Occam's Razor is pretty clearly in the same neighborhood as the contrast I was suggesting, I notice that Baker characterizes the methodological approach to Occam's Razor as facing the following practical challenge:
Justifying a methodological principle requires answering a pragmatic question: why does it make practical sense for theorists to adopt parsimonious theories? Most attention in the literature has centered on the first, epistemic question. It is easy to see how syntactic elegance in a theory can bring with it pragmatic advantages such as being more perspicuous, being easier to use and manipulate, and so on. But the case is more difficult to make for ontological parsimony. It is unclear what particular pragmatic disadvantages accrue to theories which postulate extra kinds of entities; indeed—as was mentioned in the previous section—such postulations can often bring with them striking syntactic simplification.
I quoted this passage because the sort of defense I gave for methodological simplicity was that it is easier to discover the limits of simpler theories, and (consequently) easier to learn how complex a theory must be in order to account for certain sorts of things. The methodology I described is not really the method of "adopting" a simple theory of practical purposes. It is the methodology of investigating the versatility of simple theories, without any further claim about epistemic or practical advantages of outright adopting that theory.
Baker's breakdown into epistemic and methodological seems to draw out the contrast between preferring simplicity because believing the simpler theory is a better way to arrive at true beliefs about the thing it is a theory of, versus preferring simplicity because proceeding as if the simpler theory is true is a better way to actually make predictions about and exert influence on the thing it is a theory of. My proposal, on the other hand, prefers simplicity because investigating simpler theories is a more efficient way to learn about the explanatory power of various sets of primitive resources. In itself, it carries no recommendation for believing the theory or for proceeding as if the theory were true.