Without recapturing, you're not "upconverting" anything. The files only contain so much information as you had captured originally. Look at this recent thread, which discusses a similar situation:
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www.lafcpug.org]
Graphics will look better if you create them in the new Uncompressed SD timeline, but the original image quality will not improve. Garbage In, Garbage Out. But it should look as good as the image you were editing with. If it looks worse, then you're doing something wrong -- make sure you render, check render settings, and check to make sure you were exporting the movie file with Export - QuickTime Movie, not Export - Using QuickTime Conversion, and self-contained instead of reference.
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