1. You already have the 808 and like it. If you are ready to take your racing seriously you might consider picking up a used roller that is in good condition. Not having parts available is all up to you. Total cost to you can be no more than $350 total.
2. The Mugen is a damn good car. But is it $600 better than your Xray? What if the hobby shop does not have that particular part you are looking for? IMO - serious racers always have spares no matter what car they drive.
If you like your 808 that much then take it to your LHS and show them why. Maybe they will start carrying parts for them. It could be that they do not know how good the car is.
TEX