Wouldn't it reduce the drag from the diverter and nozzle down in the water as well as free the boat up higher in the water this giving more mph at the same rpm etc?
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Not really the intended purpose, but to answer your question, not really, it's an added ride surface that when that close to the pump at an upward angle provides something for the boat/hull to "ride back on" theoretically allowing more hull to escape the drag of the water, this lowers the overall drag coefficient and increases the amount of air under the boat providing that all elusive lift.
You can move something through air a thousand times easier than water (approximately), so the more lift, the lower the Cd.
There is a fine line where you make too much lift, this is when the porpoise of death is experienced. That is where the adjustable plate shines the brightest. Well, that and a whole bunch more horsepower and weight distribution.
Edit:
But to say it can increase mph all by itself, I think that's a little misleading.
GT
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