Light Screen / Reflect doesn't raise your defenses, it just halves the damage. (It did double the defenses in Gens 1 and 2, bit Stored Power wasn't a move in Gens 1 and 2)
Also, take a look at this replay. (I forgot to invest Clefable's Special Attack EVs but oh well.) If Clefable's base Stored Power did get a boost from Light Screen/Reflect, it would've did more damage to Gengar.
Also, on the Pokemon Showdown Damage Calculator, even with Reflect and Light Screen still up, Stored Power will still have a Base Power of 20.
EDIT: Aurora Veil doesn't affect Stored Power's base power.
Hope This Helps!