If you're not an XBL Gold subscriber, then odds are the Xbox is not your primary console. It also means you can't and don't play online with it. So, the Xbox is good for single player mode and not much else.
If you need or can use the small amount of trade in value an Xbox is actually worth and you have no intention of playing any of your single player games again and/or you've already sold most or all of them, then the only reason for hanging onto an old console is if there's something in the next year you're planning on buying that hasn't been released yet.
Presumably, you have little or no money invested in any XBLA games or downloadable content either, which is really what links people to a hardware platform; the services and purchases made on said services.
Halo 4 is pretty much the swan song for the Xbox 360 as far as exclusives go. There's a prequel in Gears of War Judgement coming and another Forza title, but anyone who had even the remotest interest in MS Studio's major IPs would already know about those and would be hanging onto their Xbox, even if it wasn't their online/main console. So presumably, you're not planning on buying or playing any of those.
Personally, I don't know why any dedicated gamer would even bother to buy a new console this late into the development cycle knowing full well what it has in the back catalog, as well as what it will have until the next gen replacements arrive next year, but then I realize there are a lot of gamers on limited budgets who will actually waste more of their money buying a console to play a new release game and then sell it or trade it in for a lot less when they're done. Rinse, wash and repeat with each big exclusive title.







