The smart previews must be exported to be useful, since they are un-edited, like a raw file.
Upsizing them by a couple hundred pixels (when exporting) probably won't hurt too much, but then why not just export the raws?
PS - a plugin can replace the smart previews with a larger version (I have a plugin which replaces them with a smaller version), but as I said, there's no value in it for what you are hoping to do, if I understand you correctly.
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