Does changing dwell affect mileage? Yes. As the points wear the dwell changes and the spark timing is delayed and becomes less precise, causing more frequent incomplete burns. The first significant improvements in fuel economy resulted from electronic control of both dwell (coil charge) and spark timing in reaction to varying load and rpm, which cannot be achieved with the same agility with points and vacuum advance.

But, can you change your dwell from factory spec on a new set of points to effect greater economy? No. The best ignition improvement came with the knock sensor allowing the earliest spark at all load and rpm combos.
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-K (hope springs eternal)