Ultimate caster assistant bard?

[Karuth]

Using the Sandman bard archetype you can pull of a neat trick to make casters (especially arcane casters) in your party better. It begins at level 7. Then you get access to the bard only spells Arcane Concordance and Coordinated Effort.

Until then you have 4 feats (you technically only need 1 though). Allied Spellcaster, Stealth Synergy, Spell Focus (Div), Spell Specialization (Coordinated Effort).

With Coordinated Effort you can lend your Teamwork feats to others.
Allied Spellcaster gives you bonuses to spellcasting. If you and the other caster have the same spell you even get +1 on the caster level.
Arcane Concordance can give free metamagic to arcane spells to people around you (and +1 DC).

Now you can do this pre-fight buffing routine:
1) Cast Coordinated Effort (you can include 2 casters thanks to the Clvl increase from Spell Specialization)
2) Steal the spell you wish to boost from a friendly spellcaster.
3) Cast Arcane Concordance to extend spells (works only on arcane spells though)
4) Your caster buddies buff themselves extending their spells for free thanks to Arcane Concordance and with a +1 bonus on caster level. If they are level 7 as well and use a 1h/level buff it will last 16 hours thanks to your help (at no cost to them).
5) Steal a new spell and repeat (you have 7 rounds to do it if you want to profit from free extend. Otherwise it's +1 C lvl that only costs you 1 round of bardic performance).

As a bonus you can get access to powerful, personal only, buff spells from different classes for yourself. The build is of course most effective in a group with many casters.

During battle/adventuring you can share your other Teamwork feats as needed. You can adjust the feats you take to the group you are in.
As your level increases you can include more people with Coordinated Effort and you can take more Teamwork feats. Also Arcane Concordance will last longer and you can thus buff more spells with one casting.

Here are some nice Teamwork feats everyone profits from:
Stealth Synergy: Prevents one bad roll from exposing the party.
Shake it off: Gives a buff to all saves (up to 4)
Shielded Caster: Can help when fighting in cramped spaces where the casters can't stay at distance.

Another combo is to use Arcane Concordance for automatic Still Spell and Coordinated Effort for Stealth Synergy. Sneak up on the enemy and deliver one or more silenced area spells to the enemy (with +1 to the DC). An arcane trickster would be prefect partner for the silent killer stuff since he can sneak attack with it too.

Any thoughts how this could be made even better?
There is a version of this for non-casters too, but since the standard bard already is very good in buffing fighty people I thought the spell casting buffing version would be more interesting.

[DaedalusV]

Stealspell (Su): A sandman can use performance to steal spells from his foes and add them to his list of spells known. Once the performance is started, the bard can steal a prepared spell or a spell known from another creature with a touch attack as a standard action. The target receives a Will save (DC 10 + 1/2 the bard’s level + the bard’s Cha bonus) to negate the effect. The sandman may choose a spell to steal, but if the target does not possess the spell, the bardic performance immediately ends. Otherwise the spell stolen is random, but it is always of the highest level that the bard can cast, if possible. The target loses the prepared spell or spell known and the sandman adds it to his list of spells known for as long as the performance continues, after which it reverts to the original recipient. While stolen, the bard can cast the spell using his available spell slots. This use does not consume the stolen spell. If the bard steals another spell while a spell is stolen, the previous spell immediately reverts to its original owner. This ability requires visual components.

I don't know if I'm reading it wrong, but the part where the friendly spellcaster looses his spell while you have it makes it impossible for him to cast it with the +1 to CL So that trick's out.. Unless of course said spellcaster memorizes the spell twice

[Karuth]

Yes that is a little flaw in this. But as I said it works best when the other casters take the bard's abilities into consideration and prepare accordingly.

A cleric for example can use the doubly prepared spell to transform it into a cure spell later.
A wizard could take a feat that lets him do something similar or to transform spell slots into direct arcane attacks.

Spontaneous casters would have a problem though since the spell known is lost.