A few random comments/observations...
As already mentioned, DVD-Rs are not a good choice for backups. I have had several of these go bad in just a few years. Plus, their capacity is way too small to be useful for any decent size collection.
You really should be thinking about a full backup plan, not just your iTunes library. External HDs are pretty darn affordable. If nothing else, a monthly cloning using CCC will go a long way towards minimizing any impact caused by catastrophic failure, theft, fire, etc. (Of course, it's key to store the backup drive off premises to be truly secure.)
I prefer a 2-tier approach. I use a 2 TB disc in my MacPro to act as a Time Machine drive for my other three drives in the MP and my wife's MacMini. I also use an external 2 TB drive with 4 partitions to clone all drives (except the Time Machine backup drive) once a month using CCC. I store that HD away from home.
Seriously, you should be thinking about more than just you iTunes content.