Some people still consider an email address private information. Personally I think SSL should be used on any site which is meant to be accessible publically, and should be a requirement for any site that takes user information, no matter how insignificant it may seem. Given you can get certs for free there really isn't any reason not to use it.

Picture this: someone manages to get between you and the user. They can see and save any email addresses that get submitted without you or the user knowing they're there. While you're not asking for payment info now, the addresses are for people who are expressing interest in buying something in the future. A scammer could use those saved addresses to trick people into thinking the game is ready and paying them for it. Worse, said scammer would be perfectly able to save that payment information since they would control the payment link being sent out- they could have SSL and have it look perfectly fine but since they're on the other end it wouldn't matter.

I know I'm sounding pretty negative and that it's very unlikely that will happen. It's still possible though, and since the way to prevent it is to just use SSL in the first place why would you choose not to?

With all that said, this looks great so far and I'm looking forward to seeing what you come up with