- You should sell it on some public advertisement board IMO. Trade ins are almost never good deals, as they force you in spending money in the same shop you trade it in for, at least where I live. AFAIK Amazon works only with resellers and local shops, not sure about privates, and eBay is too feedback oriented for what you want to do (if you're a just registered user without any previous feedback, relatively no one is going to trust you, and thus buy from you).
Your best bet would be to put up a notice on a board of some kind, like what craigslist does in the US.
- Since it's a relatively new console, depending on how you kept it and on how many extras you're willing to part with (games, pads, peripherals, accessories), I'd say between 250~350 (€/$, not sure of your currency, but in that range for both anyway)
- If it's worth it or not, it's subjective. I, for one, woukd keep it. I've bought 2 Xbox and 3 Xbox 360 only to drool behind particular exclusives and to frustrate myself over power button circuit burns or RRoD-related faults. Not going to do that error again... Others may think it differently.