I think its a great idea to add special content to help support the game! Yes, I agree, pay-to-play is not a great idea for this game!
It is also important to note that the economy is getting worse, therefore prices are rocketing and probably won't get better anytime soon, so there is that...Not everyone can spend a whole lot. Buying the game is usually good enough
My idea for special content: The future moving objects that Red51 plans to add in the game(like moving windmill blades, etc.): l feel like that should be DLC! Think about it...it would be, I guess, a "luxury" in the game! But how much would this "luxury" gameplay feature really be worth? Hmm...Id say, $2.99, maybe even $3.99? It really would be up to Red51!