Blu-ray disks are made from the same materials as the common DVD or CD, just with the higher density. And the more disks you have the more chance that some of them might be corrupted after some period of time. What will be with your disks after say 10 years, 15 years? I don't know, and you don't know. For better insurance you need to backup your photos on multiple CD/DVD/Blu-Ray disks.
This is not a question of insurance but also a question of convenience. Operate with multiple disks with low I/O speed.
I guess today the price of 1 GB of HDDs is very low, so you might to consider backup your photo collection to HDD.
For example Seagate Barracuda Green (2TB) costs as low as $125. http://www.pcmag.com/article2/0,2817,2382026,00.asp
You can also consider a NAS with RAID.
Just my thoughts, probably if the collection is not large the multiple Blu-ray disks is a good option.