I ride rocky trails all the time and haven't used a swingarm skidplate in a real long time. I'v found that if I'm careful, I very rarely hit my sprocket or rotor. I was hitting my skid plate a hellava lot more than I hit my sprocket & rotor. Iv hit my skidplate so hard I'v broken off mounting bolts, then the skid has to be removed while your out deep in the woods, far away from the truck. One of the shittiest jobs is removing broken skidplate bolts out of your swingarm, trust me. A few times iv hit the skid plate so hard and so many times that it bends into the brake rotor, and then your stuck. If you've put enough miles on an ATV, sooner or later you'll be deep in the woods, banging on your skidplate with a big rock trying to bend the plate off the brake rotor. It sucks. The perfect setup is the dual sprocket guard setup with the poly brake rotor guard.
I'v bent rear brake rotors on my Banshees, but I haven't bent any on my 250R in the past 5 years I'v owned it. And if you do bend a brake rotor, its not a big deal, you can find a used brake rotor for 20 bucks. Bend the brake rotor out along the trail, just unbolt your rear brake caliper, wire tie it to the frame and ride back to the truck to put on your spare brake rotor.
Every year I usually hit one big rock in the middle of the trail. You know the rock that you see coming and you know right away that its going to be close to hitting. When you see that big rock coming, get your ass off the seat, stand up on the pegs and try to actually bunny-hop the quad over the rock, if you do hit the rock... chances are that it just puts a gnash on the edge of the brake rotor.
Iv had too many skid plates piss me off on the trails, so I'll take my chances without one.