I think a great solution would be to have 2 buttons. One to view and one to complete with a plus sign and a minus sign and a box where you can enter a number. If the number/plus sign you enter completes the quest/bad/guy/power/up - there is a popup which says 'are you sure you want to complete this quest?' then it goes to complete. If you accidently complete it then you search past quests (which you can do at the moment) and you can either press repeat (which makes the quest etc active again with no loss of points) or press revoke (which makes the quest active and revokes points awarded). With the recurring powerups you could just reduce the powerup by pressing the minus button and it automatically a reduces the amount and the points. Just a suggestion to solve some accidental completions. :)

I thought of something like this, but i fear that just a tiny button without opening the description of the quest/power-up would make it more automatic and won't have a chance to make me think or be refreshed about what that quest/power-up is all about.
I thought that instead of moving to a new page for that quest/power-up, the text with the description and buttons will open in a drop down fashion inside the main quests/power-ups page, so i can simultaneously read and complete that quest/power-up while also having a fuller picture of the other ones.

perhaps i should start a new idea here for this suggestion?

Speaking of 1 touch, I just accidentally recorded an epic win because it only takes one touch! It is the second time this has happened using a touch screen, and making a scrolling error.

Maybe you could make the lightening bolt appear only after a user has actually viewed the item.