Ok, ideas for Succubus.

Give it a more Bard like class skills list and 6 skill points a level. That way Bards who Value the use of there skills won't feel like there sacrificing that to get the template.

Make it not take away all other racial traits. That way the Draconic creature or Catfolk Bard don't feel there having to give up a bunch of potentially nice things to use this Template/class.

Make it get Bard casting per Succubus level, and make the Bard casting stack with PRC's that advance bard casting (Like Sublime Cord.), and with actual Bard levels.

Make it progress (but not in and of itself grant.) bardic Music ability's and uses and DC's.

Make it progress (but not in and of itself grant.) Bardic Knowledge/Knack.

I saw you removed the Cha to AC that the original Savage Species progression granted the Succubus. I'd suggest putting it back. Mildly helpful for casters, but very good for a Melee Snowflake Wardance+Optimized Inspire Courage Bard build, and spiffy for a sit back and use Bardic Music and cast spells/use UMD build in case something decides he looks squishy enough to one shot and hurt the nice things the party was getting form him. Which any monster with an Int of 8 or 9 could eventually figure out, and anything with an int 13 or higher has no excuse NOT to have figured out by the second round of combat.

And one last big one.

IF they take all the levels of the class/template, allow them to have a special ability that doubles there Bonuses to hit and damage form Inspire Courage, but deals None Lethal Damage too them while they use it. Yes, this is basically words of creation. But it rewards the bard by not forcing them to be Exalted good (Something a LOT of DM's punish willfully.) to get the ability, and by saving them a feat they can now invest in something else. For a Sorcerer or a Begualer or a Binder, that's nothing special. For a Bard, that is HUGH! BTW, the fact that it's HUGH is also why it's a Capstone.