My Ph.D work intersects quite significantly with Roman economic history. I've never once heard of this book, I've never been told to read it, and I've never seen it cited except in Finley. So that ought to say something.

Having now checked up on the historiography of the book, and skimmed a bit of it, I'd skip it. Rostovtzeff was at Yale, and very well respected--I've seen his name appear now and then. The thing is that even at the time reviewers noted that the book wasn't really about the Roman world, it was about the Russian Revolution, using ancient evidence to explain why a modern event had occurred. Written differently it might have been an important contribution to the historiography of how revolutionary leaders are influenced in the formation of their rhetoric.

The big problem though is simply that ancient economic history was barely in its infancy in 1926. And the book was really begun in 1918. In 1926 we had no idea how to do economic history of the ancient world. Brunt's important work figuring out how the Roman labor market worked wouldn't be for another four decades. And economic theories of the past basically consisted of classical liberalism and Marxism, both thoroughly modern theoretical frameworks. Rostovtzeff's work in general fits largely into this category. M.I. Finley gets a lot of heat these days especially from archaeologists (whom he did not get along with), but it's undeniable that The Ancient Economy (1973) completely changed forever, and for the better, how we think about the economy of the ancient world. It was Finley who first proved that the ancient economy was an agrarian one, and it was Finley who first demonstrated that ancient economic structures cannot be mapped onto modern ones (though these days there's lots of work both tearing down and rehabilitating the idea of an ancient market). Now there's been a lot of pushback against Finley, especially against his notion of Rome as the "parasite city" that extracted from the provinces and gave nothing back, a notion that we know now is completely ridiculous. But Finley's big point has held over time, that the ancient economy was a fundamentally different economy in a fundamentally different social structure, and that it cannot be understood by simply applying modern concepts of economic and social relations onto the ancient evidence. The importance of Finley's work was such that there's very little in the way of ancient economic history before him that makes much sense today. It's paradigmatic, and even if one disagrees with it it's universally acknowledged that the problem is Finley's precise arguments, not the theoretical framework that he established for how the ancient economy ought to be understood.