As much as you will get more for your money/lose less money when you sell it on, don't let that mask the value of buying new as well. Buying new you know that its going to work perfectly, and if it doesn't it can definitely be returned. You also need to consider the availability of parts. For example last round cpps an older style ego couldn't be fixed on the day because parts weren't avaliable, so it was out of action the rest of the tournament to be taken to the factory.
And finally, with all the new technology arriving nowadays you're going to be waiting longer to get a hold of it second hand, when it eventually is no longer new.