Instead of getting rid of it, why not just increase the DC?
How about DC = 20 + (Spell Level x 3)?
1st level caster with max ranks, 16 Int and a 12 Con has a +8 on his Concentration check, a first level spell's DC would be 23, so he needs a 15 on his roll--difficult, and often not worth risking.
4th level caster with max ranks, 18 Int and a 12 Con has a +12 on his check, a 2nd level spell's DC would be 26, he needs a 14--roughly as risky as before.
10th level caster with max ranks, 20 Int and a 14 Con has a +20 on his check, a 5th level spell's DC would be 35--again, risky. But, a 3rd level spell's DC would be 29, and that's a much more acceptable risk.
Dave