I do not for a number of reasons. First, I never cook by time. For ribs, I cook till the color I want is achieved, irrespective of the clock. (Occasionally I cook at 275b if I feel like a long cook; mostly I cook higher. Doesn't matter though. I cook till color is achieved.)
Another reason: I do not like meat candy. Adding sugar to the foil is not something I would ever do. I use reduced juice(s) and/or reduced stock - for flavor without much sweet.
Another reason: Same as above, I do not cook by time. Once in the foil I cook till the ribs are done - tender - while in the foil.
I dislike ribs sauced while cooking. I like the meat to stand on its own. I always make at least one sauce - but serve it on the side. I do occasionally glaze for shine, but I am talking a glaze, not a sauce.
Once the ribs are done in the foil I return them to the cooker for several minutes to firm the bark and, if using, to glaze. But either takes just a few minutes.
That's my flow.
Agave will not add much in the way of flavor; sweetness yes, flavor no.
If you've already got a lot of sweet going on you won't likely notice much flavor difference if adding yet more sugar - like the brown. Lots of sugar flattens flavors considerably, muddying them up in the process.
