Bah, Bard/Favored Soul is a fine combo.
Here are some ways to make this combo work best for you:
1) Healing Hymn Alternate Class Feature (Complete Champion, pg. 47).
This bardic music replaces your fascinate bardic music ability. When you use a bardic music use for Healing Hymn, any conjuration (healing) spell you (or a nearby ally) casts during the Hymn gets a +1 sacred bonus to the die roll for each rank you have in perform. So a 10th level character with 13 ranks in a perform skill casting Cure Light Wounds would get 1d8+5+13, or an average of 22.5 of healing from that first level spell.
2) Make your highest stat Charisma. You will get all sorts of bonuses from both classes for this.
3) Focus on buffing spells for yourself or allies, and not on attack spells. Your DCs will be low (wisdom is your Divine Favor DC mod, while Charisma is your Bardic one, and because you are multiclassing your spell levels will all be relatively low). However, both spell lists have some great self-buff and party-buff spells like Haste, Displacement, Invisibility, Divine Favor, etc.. Choose on those types of spells, not the direct attack ones that allow a save. Done properly, and when combined with Inspire Courage cranked up (see below), you are going to have a massive attack and damage bonus from various plentiful buffs.
4) Focus on Face skills (Diplomacy, Bluff, Intimidate, Sense Motive).
5) Consider the Battle Caster feat from Complete Arcane. That feat lets you wear armor of one higher grade without spell failure chance. That would allow you to wear Mithril Plate Mail and cast spells from both your classes without any spell failure chance.
6) Take a look at the
Inspire Courage Optimization thread and make sure you have at least a +3/+3 from your Inspire Courage. You will benefit from it, as will your party.
7) I know the last thing you want is yet another class to multi-class into, but if you can take a single level of Warblade or Crusader from Book of Nine Swords, and the Song of the White Raven feat, you can start your bardic music as a swift action and get off a Favored Soul or Bardic Spell or Music, or an attack, in the same round. That would be highly useful.
8) Since you have more spells than an average bard, you might consider the Lyric Spell feat from Complete Adventurer. That feat lets you convert bardic music attempts into power for casting more spells.
9) You are going to have very high saving throws. Don't be afraid to use them to help the party by drawing fire from enemy spellcasters. If you are invisible, the enemy Wizard will likely target your fighter instead of you. If you are visible and obviously helping the fighter with your bardic music, the enemy Wizard is more likely to target you instead - which is good, because you are much more likely to make your save. Heck, if you are wearing Mithril Plate and wielding a longsword, the enemy might even mistake you for the fighter, which is all the better. Just keep in mind, your hit points are relatively low, so you are not a front line fighter.
Hope that helps. I think it would make for an interesting character.