I'll throw my 2 cents in here; determining whether to dedicate more $hard drive$ space to redundancy, or risk having to recapture (both valid approaches), would be based on how much one values his/her time, and how tight a schedule one is working on. Time=Money, but how much time equals how much money is the question each one of us has to answer... possibly for each project.
I'd like to add a clarification to what CootDog said about capture speed. Technically, you need to be able to capture at least 25 Megabits per second. That is about 2.6MB/second. Any modern Firewire drive will easily handle 5MB/second, so this is not a concern. Capturing seldom poses a problem, but playback can bottleneck, because while editing, you are often playing back multiple tracks, and the clips are scattered across the drive, so the head on the drive has to move around a lot, which reduces the drive's throughput. In contrast, capturing to a dedicated drive allows the write head to just step along smoothly.
Regarding the original question: 12 to 13.5 GB/hour of captured video is minimal. One will need space for render files, final versions, etc. Generally, the rule is to double the space required to actually capture, unless you're capturing for archiving only. That means 25GB/hour would be a good planning estimate, in my experience.
Side Note: One interesting snafu with HDV is that the render files may be much larger than the original captured files. I have only edited HD, not HDV, but I presume you wouldn't want your intermediates to be MPEG2 compressed. Compressing with the Apple Intermediate Codec would result in render files that were at least 2 times as large as the HDV source.