My 2c.
I think Cho pretty much explained the basics.
However, you probably don't have a lot of money to spend (I don't know how rich your parents are, but at 16, I was pretty broke and not investing in a lot of shit), so I'd say :
- Have fun, but don't think you're playing casino, you won't double what you invested after one year or anything like that
- Spread your investments, even if the amounts are really low. The point is to have "fun", basically, if you invest 10$ in Nintendo, no matter how meaningless these 10$ are, you'll still be "interested" in how they perform. So I think high diversification is a pretty good thing to do, as it's both funny, and healthy for your investment. Obviously, it means that you should first understand what is the point of diversification : lower the risk. For that you need to build a coherent portfolio, I invite you to study a little bit the basics of market finance, just so you don't build up a retarded portfolio.
- Talking about healthiness, I think what you're trying to do is a very healthy hobby, it'll keep you interested in the company's news, and that's really cool, even though you're a bit young for that. You'll probably notice then that Nintendo looks like a really crappy investment, especially from a strategical point of view, as they're threatened from every fucking angle.
- Focus on making low profits, as silly as it sound, act like you're playing a game. However it's important to win this game, make sure your % growth is at least higher than the inflation (this is your first objective), and keep improving it step by step. You're not playing a guessing game at all, market finance is all about mathematical concepts that I think you can grasp by starting safe, and then trying to move forward, little step by little step.
So yea, basically try to diversify as much as you can, try to put your interest above your personal bias and make a check up at least every month, and a conclusive statement at the end of the year.
PS : For the second-hand market, forget about it, you need to be very patient, the prices are really high, and then they go really low... only to growth slowly towards their real prices. There are a couple of rare gems whose prices skyrocket after some years, but these are definitely not 3DS systems. It's way too recent anyway, I really don't see the point, I don't even think that the second-hand price of these things will ever be close to today's prices. Now if you're talking about the Net Present Value of such investment... I think you'll be grealty disapointed.
On the other hand, buying a WindWaker game, a Baiten Kaitos one etc.. is a really SAFE investment, that you can actually enjoy, the prices of these second-hand games have already been through the down spikes, and are only enhancing. Not only you'll be enjoying these games, but on top of that, you're guaranteed to sell them back for a better price later.
Can you do it with a dozen of 3DS ? I don't think so.
So yea, buy a SNES, and invest in games, you'll have a lot of fun and you'll be winning money, that's the perfect gaming investment in my opinion (or you can emulate, but that's less funny, and you won't be selling back ROMS right?).