If as you say, you'd rather put the grand from the 31 to something you will use, then i would agree pretty much entirely with what Ash says above: sell the lens and get something such as the DA*60-250 to go along with your kit zoom.
However, I think you may wish to give the 31 a bit more time to appreciate its value and quality. They seem to be becoming more and more difficult to find, and you wouldn't want to be in a situation where you didn't completely "test out" the lens over time. Unless something drastic happens, demand for these is high, and you can sell it later if you truly feel that keeping it in your collection simply is not worth it to you. I'm in a similar situation with my only limited, the 77. I don't use it much, but I think I've committed to keep it as I know it's ability to produce and its overall quality. I would think a "normal" lens, especially one of such quality as the 31, would always have a use for you, although that certainly may not be the case. If you can afford to keep it and buy a quality zoom to cover the range between 50 - 300 or so, I think you'd be in a good position...just my opinion
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