I'm pretty sure that some voice acting was always in their budget, I don't think they are taking money earmarked for something else and spending it on VA.
Kickstarter Update #3Will this have full voice over?
We cannot do full voice with the budget we have. At the moment, we only plan to do "important characters" with unique lines.
Also, NPCs can draw lines from a database with information and lore, and we don't want NPCs sharing the same voice, or NPCs that change their voice in the middle of a dialogue.
Larian wants to make a quality product, and if that means getting quality voice acting, that's fine too.
My main concern with voice acting is the potential for repeated merchant barks and such to quickly become grating (it's harder to ignore those than the text). Hopefully they'll save the VA for important one-off lines.