@noromance, I've read that the back of the Quads were padded to make them useable closer to the wall (those small English parlours!). When they are far enough from the wall behind them (no less than 3' they say, 5' imo) that is no longer a concern. If you remove the rear burlap but leave the felt over the tweeter strip, the back wave is now different from that of the front, with less high frequency output. The Quad can use all the help in can get in that regard, so I say remove it. Or at least try it to see if you like it.
I've seen Quads with opaque (a very, very light gray) dust covers on the rear, but never the front. I don't know if they are opaque from paint, or if that is the color of the plastic itself. Perhaps because of the charge on the ESL panels, the covers can get quite a layer of dust on them. Careful with that feather duster!
