Sell my Xbox 360 (haven't played it since March), 14 games (including PKMN White, Dissidia 012, FFI, FFIV, FFXII, FFXIII, Infinite Undiscovery, Prince of Persia: The Sands of Time, Darksiders, Devil May Cry 4, Assassin's Creed II, Assassin's Creed Brotherhood, Left 4 Dead, and Halo Reach) and my DS so I might buy a 3DS and Ocarina of Time-3D? (Please note: I have never truly played a Zelda game before) fun fact: Horace and Jasper from 101 Dalmations. They look familiar no? Spoiler Spoiler OMG it's House and Arthur Weasly!
I would sell the DS but not the 360, that's just my opinion. But if you don't play either of those then sell both.
I don't think you should sell the 360. I'm not an Xbox person, but those things aren't exactly cheap. You can just sell your DS and get a discount on buying a 3DS. At least, you should, as long as you don't get a dumb gamestop