For anything important, I wouldn't trust just
optical media. External hard
drives are so inexpensive with such a large capacity.
Storing important things on a couple instances of magnetic media, perhaps
in additional to optical, might be a safer way to preserve
them. (A couple big external drives, stored in a couple of safe, offsite,
locations etc).
And you leave them some years without turning on, the heads glue to the disk
surface and bye bye.
What about memory cards? CFs are cheap and IDE interfaces may be avaiable
for years to come :oO