So you want your bike to always be brand new? That is easy, store it in a cool dry place and NEVER ride it. If you do decide to take it for a ride, you may want to keep it out of the woods, because a bike that much power and speed could really get you into some trouble, also if you ride trails, you could cause severe damage to your stock decals due to the lack of insulation on the gas tank.
Anyways, I use a pressure washer to clean my bike, with that you could at least get mud out of your engine fins. But if you use this method, be sure to dry the water off of your engine to prevent fading.
btw, I dont think there is a product on the market that will make your xr look great.