1. The idea that the coin system should never feel 'winnable' is a very negative outlook to the game. If the player is constantly reaching a hurdle that is impossible to overcome that just leaves an overall negative impression on the player. Even RPG's which contain grinding eventually have a point where the goal is 'reached' and the player no longer needs to continue with their task, and the player gets some satisfaction for the time they put into it. It's Skinner Box stuff, but it doesn't work if the system is a consistent hurdle in the players way that cannot possibly be removed, beaten, or overcome through skill.
2. Yeah, ok, you think coins are worthless now so you've no interest in goals... that tells me you were only doing the goals in the first place because the game fed you coins for doing them. How is that a good positive thing? If you don't find the fun in the goals without being rewarded for doing them then you're not enjoying doing the goals for what they are. This is like leading players with dangling carrots, it's the difference between doing something because an achievement gives you a creative idea on how to play the game or doing it because the achievement will eventually give you gamerscore. One of these things is positive, the other is hiding a games flaws from the player.