Certainly I can understand the idea that after finding a decent demo and playing it, as a 30 year-old man with not much spare time, I just want to buy the game and don't care much about the price
I can't...
And yes, you're right, a "full" game should be sold for 15-20 bucks. I mean, the price should look "right" to the buyer: if you have a game that looks like 20 bucks and is sold at 5 people will get suspicious. But if a game looks as $5 it should be sold at $5, because no-one would pay more. And releasing a game pack is a bad idea because you will get much more traffic by releasing them separately.
I heard some people that said they're going to buy it because the price is right (3 or 4), many appreciated that.
I would never buy this game for 20$, because it's way too simple, but I could consider buying it for 5$ because it offers some elements that are not in any other game and the physics are cool.
I still have to decide which sites to submit it to: If you could submit it to 5 sites only, which would they be?