I would rule that a metamagiced spell stored in any item is treated the same as any other spell that required the same slot from the caster. So a maximized first level spell would need to be stored in a fourth level spell storing item.
How do Metamagic feats effect the spells that are able to be stored in a Spell Storing weapon? My assumption is that the modified spell level is used. Meaning you can't store a Maximized 1st level spell as the Maximized feat adds 3 to the spell level.
Am I correct in my thinking?
That is my interpretation also.
An empowered shocking grasp is a 3rd level spell, and could be stored in the weapon. 26.25 avg. damage.
A vampiric touch spell could do anywhere from 7 to 35 avg. damage to your foe, and hand those hit points to you. Not a bad thing for squishy characters forced to melee!
Intensified Rime Spell'd Shocking Grasp (cast as a cold spell by an Evoker)
35 avg. damage (60 max) plus the enemy is entangled for two rounds.
Just an intensified shocking grasp works well on its own...10d6? For a level 2 slot? Not shabby.
Toppling Magic Missile can be fun, too.