TomVD

Also, have you considering using a c/c++ lib that compiles for android/ios (such as orx)?

Not really. Perhaps if I would own a mobile device with Android or iOS on it, then I would know what I'm writing a game for. I'm stuck in the age where people use their phone to make phone calls *blush*
Also I'm used to code in Java (using Eclipse) at work (business applications), so for writing an Android game I would use Java (using Eclipse).

Thanks for your quick reply.
My goal was "getting it made" at first. But I'm not afraid to learn new technologies. If the game appears to be suited for mobile or web, which is what I hear from people a lot, it might be worth the effort. Earning money is not a goal, so that's already an advantage

I have never seen that Construct tool before, I'll give it a try. Maybe prototyping the game gives me new insights.

It's rather abstract... so if I understand right, you let the world evolve while the player is playing it? Not like the usual world generator where the world is generated once at the start, but after that it's only the player changing the world.

It might be interesting to see the ecosystem behave in a reaction to what the player does. Perhaps the player is not seeing the tier 1 resource you call "energy", but his actions could alter it?
Also, do you have a goal or story in mind? There is an ecosystem, but that alone doesn't sound like a "game".

Let's call it "voxel style graphics sandbox games"

If you are afraid of making something people will be bored with, you can always try something original

An option might be to replace the graphical style, then you end up with a sandbox game where you have to invent other ways people can be creative. Perhaps you can let them pump up oil that is used to mold plastic objects. Have this little crafting interface which is a very simplified 3D modelling tool.
Make sure people can easely put up screenshots or youtube video's of their creations, because the whole purpose is to show off your creations

Or replace the "sandbox" part and make it a race game (cars with square wheels, must be funny), an fps or a tycoon game perhaps.

The only problem I have with the freemium model is in cases where you add up all premium content you come to a large sum (>100$) and they can tell you that you don't HAVE to buy all the premium content, eventually a lot of people do, because of the feeling to miss out on something.

It's a cheap trick to earn more money on people that have this urge to collect everything of a series. An extreme example is the downloadable content of Train Simulator, you can pay up to 1000$ to download every train in the game. I'm sure some people do... I'm afraid.