I don't think it's too late to improve the quality of the VO for a 4th game. There wouldn't be many legitimate complaints from fans if the game had really good VO, and it'd give the game a better chance of success.
Honestly, most of the characters in S3 were solidly voiced, if a little exaggerated, and a huge step up from the Dreamcast games. Unfortunately, the localisation didn't really improve along with it, and there were key characters, like Shenhua, who kinda ruin it (I don't blame the voice actor).