Maybe for now not really.
I am a new fan but I've been listening to Kara4 songs these days and I love it.
The thing is, now they show themselves as a 5 people group and no longer being called 2nd Fin.K.L so it will be best if they just stick to Kara5 songs.
Perhaps if they have a Kara Concert, and Sunghee is invited as a VIP guest and they can have the open stage with Kara4 performing the old songs.
Great idea? =p