Need help with homebrew ability/feat

[Adamantly d20]

"Persistent Power
1/day + Int
May expend an additional spell slot to increase the Save DC of the spell cast by an amount equal to 2+ the level of the spell sacrificed. At 11th level you may use this ability to expend 2 slots gaining half the bonus from the second additional spell expended in addition to the normal."

Basically similar to Psionics expending additional powerpoints to increase DC does it seem balanced (this is intended for 3.5/pathfinder)

[aimlessPolymath]

Verdict: Pretty busted.
Abilities are balanced around a progression of DC 10+1/2 level +stat for a reason, and this breaks that wide open. Unlike many feats, it gets exponentially more powerful as you level, it makes 1st and 2nd level spell slots super powerful, etc.

[brian 333]

See the Fox's Cunning spell, which is very low level with a duration of 1 hour per level, (almost half a day for your level 11 guy.) 1d4+1 bonus Int for half a day is pretty sweet.

[Adamantly d20]

What if you had it give only 2 + 1/2 the spell level bonus instead.

[NikolaTesla]

What if you had it give only 2 + 1/2 the spell level bonus instead.

To put it further in perspective, consider the feat spell focus from 3.5 (I don't play 5e so I don't know if it still exists).

At the cost of a feat, you get a +1 bonus on only one school of magic.

Even with that adjustment I can just spend one of my near worthless first level spells and get and instant +2 bonus to the DC for ANY school of magic. Very broken, especially when you consider that I could sacrifice an 8th level spell to get a +6 bonus to the DC of an "I win button" spell.

[Adamantly d20]

Thank you for the input. Much appreciated. I guess it needs to be heavily nerfed and limited. Maybe ability damage backlash from using it? And like once a day.