My "paragon bar" appears to be full but I continue to receive paragon points. Is there a maximum amount of paragon/renegade points you can receive? If not, is there any benefit in obtaining any more once you have filled the bar?
The Paragon / Renegade system in Mass Effect 2 is a bit different than that of Mass Effect 1. In the earlier game, Renegade / Paragon actions were available explicitly based on your charm / intimidate score.
Mass Effect 2 removed both alignment based skills, and instead calculates available dialog paths based on earned paragon/renegade points / total potential paragon/renegade points up until that point.
I'll quote directly from the mass effect wiki:
The morality system of Mass Effect 2 works on percentages rather than the total points earned. There is a set number of morality points available in the game. Shepard's current "effective" morality score at any given point is the number of points earned out of the number of points available from the areas he has explored so far. It is possible to have Shepard's Paragon/Renegade scale(s) maxed out, but still not have the percentage required for certain dialog options.
So even though you are no longer filling the bar, you must continue to act as a paragon, or else your percentage will decrease over time, eventually locking you out of some paragon dialogs entirely, as you continue to miss out on potential paragon points.
The Paragon / Renegade points carried over from a ME 1 save file are an exception to this rule: For instance, if you start the game with 50 paragon points from mass effect 1, your paragon score is
50 / 0 (ignore the potential divide by zero) instead of
50/50if you had accrued those 50 paragon points through normal ME 2 gameplay.
The maximum amount of renegade/paragon is unlimited. This means you can continue to gain renegade or paragon points indefinitely without any affect on the game.
80% full is the maximum worth you can gain out of both paragon and renegade, upon reaching that point it provides no more value (so at that point it helps to level the other one)
Here is some reading material if you want to know more.
Hope this helps!