I'm also gaining a new appreciation for how hard Romans is to interpret. As I study I've been consulting a 1,000 page commentary. Incredibly, there are places where the exegesis feels rushed, where complex counter-arguments are glossed over in a few sentences. In those places I catch a glimpse of the larger world of Romans interpretation that could fill volumes, and into which 1,000 pages can only present a tiny window.
The difficulties notwithstanding, however, I think I've found a broad principle that focuses many of the disagreements: Paul's treatment of corporate and individual. That is, which passages in Romans have personal, individual application? Which refer specifically to redemptive communities (eg. Jews, Gentiles, the Church) and can't be directly applied to individual Christians?
This question is at the heart of some of the most controversial passages in Romans: ch. 7 (is Paul describing himself, or speaking archetypally of the nation of Israel?), ch. 9 (does God elect individuals, or communities?), and many others.
These are not easy questions. The line between corporate and individual in Romans often seems very thin. As an example, consider Rom. 11:17-21:
But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. Then you will say, “Branches were broken off so that I might be grafted in.” That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but fear. For if God did not spare the natural branches, neither will he spare you.In context, this seems clearly to have corporate application: gentiles as a people-group are being grafted into the nation of Israel. And yet to read the passage strictly in this light implies that Paul is threatening the gentiles en masse, as a group, of expulsion from the people of God if they (corporately) do not stand firm in their faith. This flies in the face of everything Paul has said previously about the inclusion of the Gentiles as the culmination of God's plan of salvation, and sounds plain weird besides. It seems much more likely that Paul is warning individuals against the danger of apostasy, even though his metaphor is corporate.
The observation that many of Roman's interpretive issues involve discriminating between corporate and individual application doesn't make those decisions any easier, but it does link them in an interesting way. Assuming that Paul has more or less the same focus in mind throughout the letter, one's opinion on whether or not Paul is describing himself in Romans 7 may have implications for Romans 9, and vice versa. This widens the relevant context significantly: it may be really hard to understand a particular passage, but getting a feel for what the entire letter implies about the corporate and the individual may impose an interpretation on the passage in question, or at least limit the viable options. And this can be a significant help in navigating the depth and breadth of Paul's letter to the Romans.