I read just about any paper about theories of comics I can get my hands on — some are pretty good, but some leave a lot to be desired. This should maybe be expected from a still-burgeoning field. Usually, when aspects of a paper have troubles, there are some consistent problems. So, here's some advice for potential "comic theorists":
1) Don't cast your theories so wide they are difficult to validate. Broad sweeping claims should only be made if they can be backed up by examples and/or citations. It's better to be specific and explicit in your theories.
2) If you're going to create a theory about comics, base it on the properties found by analyzing actual comics instead of pure theorizing. Often times people get so involved dreaming up of logical possibilities that could occur (or borrowing them from other theories) that they don't notice what does occur. At the very least...
3) Test your theory on actual comics (lots of them!). If you don't find your theory accounts for things you find going on in them, modify your theory appropriately.
4) Develop your theory with conventional examples, not exceptions. Often times the exceptions make for the most interesting examples, because they are noticeably different than "normal" usage. Granted, you can use those exceptions as clues to how conventional aspects of the medium work. However, if your theory is just about exceptions, it won't generalize to "normal" aspects of the medium too.