Ectoplasm, like fainting spell, occurs during your turn when you knock out the defending pokemon. Since power spray is used during your opponent's turn, you can not use it to negate the actication of that poke power.
With Torterra, leveling up removes the status of not being able to attack that was placed by the attack itself. The pokepower text states that you can use it once per turn. The pokepower effect is not a status, and as such, will not be removed by leveling up.
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