Copying files does not affect quality.
Opening and SAVING files loses quality - even if you don't edit them.

I would not rely on DVD copies alone.
I have had bad drives, that write discs but can't read them reliably - but they work on another drive.
I have had bad discs, that write and verify as OK - but verify slowly and can't be read on other drives.
This is on 3 or 4 computers, Dell by far being the worst for DVD drive quality.

I now use a BENQ drive, bought as an internal drive, then put in an external USB case with good ventilation and a fan. It is good quality, and I haven't had any errors.

BUT don't rely on only one backup ... Make more than one.
Don't keep them in the same place, either.
If the worst happens (home fire) you'll be glad you had a backup in the garage.

I have multiple layers of backup.
1) working storage on 4TB NAS, RAID 5 - protected against single disk failure
2) automatically copied to second 4TB NAS, RAID 5.
3) automatically copies this year's RAW, JPG and XMP files to third 3TB NAS, RAID 5.

All files up to August 2009 copied to 2TB external drive and that drive put away for Archive.

I think I'm covered.
But I plan to put a NAS somewhere else, and backup to it across the internet, automatically, each day. I just need to find a safe place for it.