I feel as though that will cause more conflict as all the players ask you what the hell you're doing, and make people spend more time on their sheets as now they will be taking things which make good use of their power points rather than thematic variations (no archers with trick shots, no martial artists, no Iron Man suits, etc... well, not necessarily none, but these are all the sorts of things that might typically make good use of (Dynamic) Alternative Effect). It may be a little counterproductive, that's all.
If you're not allowing Alternative Effect, are you also removing utility belts, flamethrowers, etc?
As for the numbers, you may as well pluck something out of the air. Try building a character using Alternative Effect and see how many points you saved... however, if you then try building that character without Alternative Effect, you'll probably find that it's more effective to spend your extra points in different ways.