I can see two intrepretations:
(1) The variable, numeric effect of cure light wounds is the damage healed. It doesn't matter that the amount healed is a constant plus a variable range, you calculate the normal amount of HP healed, and then multiply it by 1.5.
(2) Each component of the damage a spell does can be considered separately. Because only VARIABLE effects of a spell are magnified from Empower spell, an empowered cure light wounds only does (1d8*1.5) + level, since it only affects the variable portion of the damage. Anything that is constant is not multiplied.
Given that the magic missile example is contrary to (2), I think it has to be (1).
So, empowered Fire seeds (holly berry bombs) would be (1d8 + level) * 1.5. After all, even at caster level 20, the average is only about 14 extra damage. Not even worth it probably.
Now, empowered Fire seeds (acorn grenades) is a different matter (at least, according to the SRD): a total of (20d8 * 1.5) damage is nothing to sneeze at, even with heavy resistances. If you can hit the target with the ranged touch, that's an average of 135 fire damage, with no save. Even with bucketloads of fire resistance, that will definitely sting a little.