If you aren't using the 35 and 50, it would be worth selling them, although, I would prefer a combination of the DA* 55 with the FA 31 than the FA 43 with the FA 31. As others have said, the focal lengths are pretty close and you do lose a little bit in speed as well.
The biggest question is one of focal length. Do you like 30-ish mm lenses and would you shoot it enough to justify the outlay of funds? Sounds like LBA is working though and you're best off giving in, since that disease can be paralyzing in the worst of circumstances.