After some thought, I don't care which tier of powers get submitted.
Tier 1: Roll it. NO durations longer (generally) than a round (unless it is something weird like freeze fade). No 'combat' no 'till nightfall' etc. Multiple rounds cost MP per round as you can see with the examples given.
Tier 2: Once per mission. If I just stick the ideas into the graveyard it means either 'already got it developed, trashing this' or that it is so far out there I would never consider putting it in.