I would think the "don't change locale" policy would apply to the global plugin locale file, because you would need that file translated into all languages just like the main file.
I think 300KB of RAM on every request is a lot. I do like the suggestion of separating the admin strings, to lower the user view. Presumably the admin side would load both sets, and the user side just one set. LifeType is on the heavier side of things, and the lower the requirements we can make on the server, the better.