The main question is what your current lenses are not doing for you. Based on the community feedback, the FA 80-320 is generally considered a decent lens, so the DA 55-300 may not be a clear-cut upgrade in every respect.

The DA 55-300 is another consumer telephoto zoom. Its advantage is convenience: it starts wider at 55mm, so it could reduce the need to swap between the 50-200 and 80-320. Optically, it seems to perform quite well at the shorter end, but one user noted softness at the long end unless stopped down to around f/10.

So, if your goal is to consolidate two lenses into one and gain a more useful zoom range, the 55-300 could make sense. If you're expecting a dramatic improvement in sharpness or overall image quality over the FA 80-320, the available feedback doesn't strongly support that. Before upgrading, it helps to identify whether your real need is better image quality, faster autofocus, less lens swapping, or simply a more convenient range.