- Encounter Spell: You can choose to have any number of spells you prepare after a long rest to be affected by this feat. The effects of a spell affected by this feat change to its "encounter" entry. If you cast the spell, instead of losing it, you regain its use after a short rest.
- Empowered Cantrip: You can choose any number of minor spells to be affected by this feat at the end of a long rest. Affected spells' entries change to that of their "empowered" entry.
Burning Hands Encounter entry: This spell's base damage is reduced to half, and its damage when saved against is reduced to half the new base damage.
Magic Missile Empowered Entry: This spell's damage increases to 2d4+2, but you can use it only 4 times per day, plus 1 additional time per the level of the class you took a level in when you gained this spell. You can expend multiple uses of this spell as an action to create that many missiles, which can be directed towards the same or different targets.
P.S: Since spells will scale as you use higher level spell slots/spend more willpower on them, (with a spell's "level" becoming the minimum level of its spell slot) I don't think making meta-magic affected spells be treated as one level higher by default will be necessary, except for spells affected by maximize spell, enlarge spell, etc.
Wizards should get an extra meta-magic feat whenever they take a level in wizard when they would gain a feat, but meta-magic feats should be available to all spellcasting classes, including clerics, druids, etc.