I use the equip quest item addon that gives you an "select this reward and equip it" button on quest turn in, and then I cycle through the whole team using the "next slot" keybind. (isboxer).

Quest receipt is probably the only place I really care about having visible slave windows at all, but there is nothing more annoying than finishing a quest on 4 toons just to see that one toon couldn't be bothered to pick it up. Having the four visible quest dialogues visible out of the corner of my eye helps to cut down on that. If there is anything that I really want to see from the slaves, I pipe it in on my main screen through videofx's. For example in lotro I piped in quest trackers, cast bars, and mini maps all around the main toon.

I agree with khatovar, screen real estate spent on browser/media player is more useful than extra slave visuals.