I think we need some sort of indication, when clicking on a dialogue choice or an interrupt, what exactly is likely to happen. I just wouldn't use paragon/renegade points to lock out dialogue choices, and I'd implement a factional and/or personal approval system similar to what was used in Fallout: New Vegas (for factions) or the Dragon Age games (for other characters), with the approvals driving changes in how people react to you rather than the paragon/renegade ratings.
Part of the problem with paragon/renegade is that it variously reflected different and sometimes incompatible contrasts: conciliatory vs. confrontational, principled vs. expedient, and sometimes multilateralist vs. unilateralist in how Shepard relates to other species and organizations. Sometimes being principled and multilateralist requires chewing somebody out, as I usually do to Gerrel for his warmongering in ME3, and yet I ended up getting renegade points for it at one point. (And I didn't punch him, I just yelled at him after he fired on the dreadnought while Shepard's squad was still on board.)
Instead of getting morality points for yelling at Gerrel, maybe Shepard would get something like:
Legion +5
Koris +2
Tali +1
Gerrel -3
Or maybe:
Geth +5
Civilian Fleet +2
Heavy Fleet -3
And this in turn would affect the different ways in which Shepard can negotiate geth/quarian peace later, with it becoming impossible if Shepard has negative ratings from most of the key characters/factions at the end of the Rannoch missions.