I replaced mine. I hated that stock stuff anyway...
I used the same stuff that is in the back bumper, but with slightly larger openings (and galvanized). A bit time consuming, but relatively easy job. FYI this is pretty much the stuff they use for reinforcing concrete - you can pick it up at a hardware store.
Basically I cut a big sheet of it, then painted it with Pasti-dip (
www.plastidip.com). This gives it a nice rubberized coating that resists chips and will bend when you start shaping the piece.
I used a tube of black urethane adhesive to secure it back in place as well (looks like that's how the factory did it). Although their stuff is REALLY tough to cut away...
Anyway, its a bit rough on the hands, but I think mine looks really nice afterwards, much better than stock.
As far as removing the bumper cover itself (and you really do want to do it first), it is described well in the manual, but basically there are four large bolts/nuts that hold it in place. Two are difficult to get to as they are under the headlight pods. The other difficulty is getting the fasteners around the wheel liners loose, since everything tends to rust, and fiberglass breaks loose easier than rusted hardware!