With "normal" power levels the stock glassfiber spar is quite adequate (mine has about 150W). If you feel like using carbon, you can.

Other's have managed to break the tail behind the wing, so that is one area you might look at if you want to do reinforcements. I just smashed the nose a couple of times, before I got the hang of flying low wing planes... I suppose a solid block of steel would have survived those "arrivals" OK.