When you capture the DV tape, which format settings do you use?
When you import the video to the timeline, is it as 640x480 or 1440x1080? Alternatively, might there be a first frame in the project which is 640x480 and therefore causing the whole project to default to standard definition?
I suspect your project parameters are somehow being set to standard definition. The maximum bitrate for a standard definition disc project is 12,500, even if the destination media is BD. Studio allows higher bitrates only if the project parameters are HD.
An upgrade to quad core should not be mandatory in your case, unless your projects get huge, since the HV30 shoots int HDV-MPEG2. Right?