Crash bars will protect the engine from damage if the bars extend to the lower areas. Upper crash bars may protect the plastics but not the engine case itself. If you're only on pavement you probably don't need to get full crash bars. For riding on trails where there could be uneven protrusions like rocks, I prefer to have the full crash bars. Crash bars will protect the engine from potential damage if hit by a vehicle or sliding into the curb, so they may still be useful for the street.
Note that the front turn signals will hit the ground in a tip over and crack the expensive plastic fairing. They stick out beyond the protection of the handle bars. Even with frame sliders or crash bars. I suggest replacing them with micro sized LED signals like those from R&G Racing. LEDs are brighter. You'll need a cheap load adapter that plugs into the original wiring harness and then plug the new signal into it. Cheap and as simple as it could be. You'll need an adapter plate to mount the signal, which R&G sells cheap or you can make your own out of a piece of plastic.
+1 crash bars. buy crash bars considering what engine components are sticking out and could be damaged. no wrecks, but a few fall overs and tip overs on my 2008. the hepco beckers did the trick, in combination with the other protruding "protective" points on the bike.