I'm afraid I have some bad news for you. You've got the right idea in utilizing the "scale to frame size" option as that would have automatically adjusted all your footage to fill the 1920x1080 sequence without actually adjusting the scale parameter. The problem is that function only works at the import level, meaning that turning this option on doesn't affect any of the media you've already imported. I'm afraid you're stuck with manually scaling everything and then fixing it once you relink, as far as I know.
Well thanks for the reply, I was afraid of that. It's not a huge deal as there's only probably 150 clips for half an hour of total footage, might as well learn that lesson now before I edit something bigger.
I did notice that the scale to frame size option only made the clip resolution as large as the smallest size of the final desired resolution, resulting in black bars on the right and left of the video. Is there a way to force it to conform to the maximum resolution size of your sequence, even if that means cropping slightly?