As first questions go these two are quite deep! I'll take a whack at them
What's your opinion of the epistemological worth of economic theories, specifically the ones you have studied and have significant knowledge of (I'll leave you to define significant)
Like a philosopher would do, the first question is to ask "epistemological worth". Let us take it as its ability to justify its results as knowledge. Of course I was reading a book about how economics is not a science, but that does not mean it has no epistemological worth. Rosenberg, who wrote the book, starts it out explictly saying he wants to show economics and economists' accepted standard for knowledge - science is best - are incompatible. (He's also an outspoken atheist, if that means anything.)
The book is also twenty years old and it shows. Its greatest criticisms are hurled at general equilibrium theory, the demonstration of how all the markets in our economy can clear simultaneously. In terms of further research potential, it is also dead. Economics have moved on to field experiments, of having people play games in labs to test micro theory and of randomized controlled trials (RCTs) to figure out which policies work best on target populations.
Is it any better at prediction, though? Not really. Now it's game theory which has to come to terms with incorporating information in its theories, inventing a bunch of new equilibrium concepts along the way. At least one game theorist, Ariel Rubinstein, has come out and said game theory cannot predict anything. RCTs is one of many ways in which econometricians, understanding the potentially infinite ways tastes and expectations can confound estimated effects, solve the problem not by inventing better methods but by limiting the scope of their questions. An RCT on building wells in a Kenyan county gives information to the officials in said Kenyan well, but is not generalizable elsewhere.
I have left out one obvious angle: the predictive ability of macroeconomics. Even though most conventional models failed to predict the financial crisis, you could also say that models lead to insight behind the "Great Moderation", about three decades of lower volatility in the economy. It could also be practically better to have predictions than to have none at all. Yet to say macro theory is superior over doomsayers and goldbugs isn't saying much, since in many of those other cases there is no standard for which the doomsayers use to accept or reject evidence. That doesn't mean macroeconomists have a standard that isn't objectionable.
There is a sense in which economic theory, being logically consistent, is trivially knowledge. But I do not know about economic theory's ability to set a standard that someone can employ to figure out true facts about the world. Economic theory tells you a few "deep truths" about how people behave in a market economy - but how do those deep truths relate with culture, biases, "shallow truths"? Theory can control for them and model them, but you still have no standard that can reject propositions like "the culture of social group X matters among X."
Economists are more about pulling the blinds over the possible, implementers of beliefs. Some libertarian economists, who advocate for the abolition of certain policies, are testament to this fact: the goal of their research on a world tainted by these policies is to conceive a world where their research cannot be a standard for thinking about it.
