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From my experience, when playing Aria, it's best to start the game by maxing out Attack, then gradually increase Attack Regen and Upkeep. Aria's homing missiles are her strongest feat and you should keep the attack gauge and 3rd (top) level all the time.
In case of Noire, you may want to try Magic Regen and Upkeep more, as her spell actually deals a lot of damage. Don't completely ignore your Attack stats, but Noire should be able to stand her ground a lot easier with magic improved.
When fighting the second boss, attack the robots (not the boss) during the first phase. When you already kill 4, there should be small enough number of bullets on the screen for you to take a moment and regenerate. Kill the 5th one to proceed to further phases.
Whenever you fire a spell, position yourself right under the boss and fire away, to take as much of his HP as you can during your invulnerability period. This applies especially to Noire - when doing this trick with her, do not use focus. Use normal fire - you will have more bullets this way, and if you combine the freezing spell with it, your attack power will be enormous. Remember you can also hold the spell to last longer (watch out for your magic gauge though). Use this to beat the most problematic phases! On each phase the boss will give you powerups, which should help you regenerate lost magic.