I command you on your redundency efforts.
But at $70/1TB for a decent external HDD, your tapes are not only inconvenient to use (have to do everything real time), but they're actually much more expensive, as it takes about 84 tapes to store the same amount of data (~12GB per tape). At $2 each (which is not HDV grade at that price, whatever that means), that would cost you over double what HDD space costs.
You might bring the fact that the HDD medium is more prone to failures, but tapes aren't perfect either (I've experienced data corruption within 5 years, that might not be typical, but it happened to me). For the price difference, you can rest assured that you'll be able to move your data every 5 years for cheaper (in 5 years time frame, I suspect 10TB will be at around $100). While your tapes are probably going to go up in price since there are less and less camcorders using them on the market. Note that no DV or HDV consumer camcorder were announced in 2010 from any company. And let's not forget that you'll have to keep that tape-based camcorder in working order to be able to use the tapes if you ever need them. That's still possible right now, though somewhat harder already (try to find a new HDV cam right now, it's not easy). Now, think in 5 years? 10 years? 20 years? Bottom line, your HDD content is medium agnostic... you can easily transfer it to whatever cool medium will come in the future using any current or future PC. You tapes on the other hand are tied up to the HDV miniDV medium and will require hardware and lots of time to transfer.