If Claudia's case is ever officially solved my personal feeling is the motive will seem insignificant in comparison to taking someones life, and the subsequent ongoing interest in her case.
I don't want to get into other cases here, but when I'm looking into other murder cases I'm often shocked at the motives people have for taking the life of another.
With Claudia, although I think the people actually involved was likely no more than 2, I personally believe there were others who weren't too happy with how things were going, and things that got spoken about after a few drinks. If I'm right, I think it could have given the actual perpetrators a feeling that they were doing everyone a favour in removing Claudia from the situation. Like I say, only my opinion based on articles like this
Revealed: Missing chef Claudia's '40 different men' in which friends are quoted as talking about how her behaviour changed after drinking alcohol, and also how she thought going after married men was just a bit of fun. And this one
Missing chef Claudia Lawrence's best pal tells of heartbreaking 10-year search where JK talks about Claudia always being worried she had said the wrong thing while she was drinking.