but would it be crazy to just capture a photo from the live preview instead of going through takePhoto?
It would be crazy with the library as it stands, simply because I don't expose the preview frames. :-) That's on the issue list.
it looks like you have a FullExifFixup for all Samsung devices, but I'm having different behavior between my S2 and S4
I don't have an S2 at the moment. If you can provide me with a reproducible test case (including details of the specific model of S2), post an issue, and I can see what I can do.
I'm wondering if it wouldn't just be easier to grab the preview image
It won't be at full resolution of the camera -- you'll be capped at the preview frame size. That being said, plenty of apps work with just the preview frames. Vine, for example, captures its video by capturing the preview frames, due to various problems they ran into when using MediaRecorder
(there's a conference talk from a Vine employee that goes into more details).