Currently it takes a halfling 20 enhancement points to receive a +4 to hit and +8 to damage on a opponent under combat advantage.
Compared to a half elf who can get more sneak attack damage with the rogue dilettante for only 6 action points. Of course this doesn't stack with rogue levels or give a bonus to hit but the cost makes much more sense.
I would suggest changing the halfling bonus in one of three ways to make it more appealing.
1. Half the cost to 10 action points from 20. If this is too powerful a change see option 2.
2. Make it cost double the half elf cost because of the bonus to hit, so 12 action points.
3. Change it so the cunning enhancements are no longer a requisite to take the guile line.
I welcome other ideas as well so please leave your feedback.