You rarely see clerics attempt to turn undead past level 8 or so and very rarely a turning spec'd cleric. I believe this is because mob hit dice scales up much faster than the cleric (or paladin) can gain turning prowess. I've tried to think up a couple ideas of how to improve turning without the need to make a pass over all the undead mobs, but rather by altering a couple feats/enhancements.
Imp Turning Feat:
Make this scale. A couple options for this would be:
6 point scale: This feat adds 1 cleric/paladin level for turning calculations and another at 4, 8, 12, 16 and 20 cleric/paladin levels.
5 poitn scale: This feat adds 1 cleric/paladin level for turning calculations and another at 5, 10, 15, 20.
The feat could also be made on a 4 point scale. I think this would make the feat much more valuable as it remains somewhat useful at high level where the undead have many more hit die.
Imp Turning Enhancements:
Imp turning I: 1 AP, this enhancement adds 1 cleric/paladin level for turning calculations.
Imp turning II: 2 AP, this enhancement adds 2 cleric/paladin levels for turning calculations. This stacks with IT1 brining the total to 3.
Imp turning III: 3 AP, this enhancement adds 3 cleric/paladin levels for turning calculations. This stacks for a total of 6.
Imp turning IV. 4 AP, this enhancement adds 4 cleric/paladin levels for turning calculations. This stacks for a total of 10.
This is different than most enhancement chains in terms of cost per point gained. This is intentional because of the rate at which undead hit die scale.
Seek eternal rest spell:
Make it scale. Start at the current +4 sacred bonus, then add 1 sacred bonus per 3 cleric levels. Then let the spell stack with the highest item worn.
I'm hoping that one, some or all of these are easier to do than adjusting the hit die of all undead. i.e. By focusing on one feat, one enhancement chain and one spell instead of a full mob pass.
Discuss.