I think you get points based on how many gold you use in the event. For example using 99 gold to one click open all the shells, will get you 99 points.
Yes, every gold you spend in that event counts towards the points. Doesnt matter if you choose the reward(which is better overall) and then uncover all to get it in the next round (which is kind of stupid if you ask me.. you choose reward but you need to either uncover all or reset to get to the next round where you finally get it...), you can individually if you feel really lucky and know that you spend less gold that way.