Unless you have terrible luck with receivers, paying the $15 is a better deal than the protection plan.
If you have your receiver for 6 years before it breaks:
With the protection plan ($6/month, before the recent increases): $432 (over the 6 years)
Without the protection plan: $15
Unless you are going through a receiver every 2 months, it's a better deal to just pay the one time fee. This obviously does not include any tech visits, but if you are technically inclined enough to be able to troubleshoot a dying HDD, you likely wouldn't need tech visits anyway.
On the note of backing up your recordings: can you use an imaging program to image/copy the EHD? I imagine a program that does a sector level image or copy could copy the EHD, even if files or file system are not readable by the computer.
Edit: Holy zombie thread...
The Protection Plan is a big waste and I've thought about taking it off of my account numerous times but I will say this being on the protection plan I have never been charged $15 for a tech visit, they have always been free. Besides upgrading my service though (from SD to HD then to WA to EA) I think the whole time I've had DISH out here since 2005 is maybe five times with most of them being after my switch from the WA to EA when my DMA added HD in the EA in 2012.