Everybody has gone H264 for video these days and that pushes the Xbox XBMC builds to breaking. If you have all Xvid and will continue to rip to that then it could be an option.
XBMC on a raspberry pi would probably represent a better option If you have a couple of hundred then a PC will do all that and have trivial access to every streaming service, probably with the best selection and UI to boot.
As for the xbox if it works then do not scrap it -- if you have a softmod already then you are spared most of the aggro with modding them (give or take the hard drive replacement). Mod it and give it to someone that wants it. Even if their media options are not the best these days they still make good emulation boxes, even on a stock hard drive.