Considering there haven't really been a great deal of actual ideas offered aside from romance or redemption, I thought I would toss some of my ideas out to you Wes.
The issue of having Valen react to Bodhi's death has been brought up. Her perhaps Valen should become a bit unstable when her Mistress first tosses her aside like garbage in Spellhold. Random banters between her and the other characters, as they would no doubt become a bit more uneasy around a crazed vampire. Perhaps having the PC take note of her growing condition and question the safety of him/her self while they sleep.
All in all Valen would hold a deep grudge for the PC, possibly thinking it was all their fault for her Mistress to toss her aside as she had. When it came time for the final battle with her Mistress, perhaps having Valen go out of control and aim to show her Mistress just how powerful she had become, in some twisted attempt at convincing her to take her back.
When her Mistress rests in her final death, and her heart being removed, Valen would be devastated. She would more then likely leave the group in shock and mixed within her own insanity, causing the party yet another delay in their course.(if they so choose to keep Valen in the group.) Upon finding Valen, the PC would be promptly assaulted by the crazed Vampire forcing them to strike her down and bringing her back to some level of sanity and realization of her new freedom before allowing the PC to deliver the killing blow. This would give Valen the chance to pledge an oath to the PC, agreeing to follow him/her through the rest of their travels. Valen would become more self dependant, though it would create a sort of hatred and at the same time respect for the PC, because of what happened to her Mistress. She would drive herself to gain power, as nothing else mattered anymore. Perhaps later down the road, she would take a small amount of revenge upon the PC by killing their romance interest or Imoen, if either were present in the group claiming they had attempted the PC's death while they slept.
Just a few ideas I thought would be interesting.