Backup Strategy

Hello,
excuse my bad english, I hope I can explain what my problem is.
I'm new to SuperDuper! and I think it's a very good tool. Making a clone of the internal system disk is easy, and this is good for a disaster recovery.
But I also have other needs for a backup. There are large data collections, like my iTunes music library, or my iPhoto photo library, which should be preserved for a long long time. These libraries are very large, and if something is missing I will detect it very late. Too late to get it recovered from my clone which is updated dayly or weekly.
So I think I need more backup sets for such libraries.

My internal disc is 160 GB and my external drive also has 160 GB. This seems to be good for a mirror, but this 160 GB are seldom used. Maybe 40 GB are used for regular files, the rest is only used temporary for conversion of audio and video files. Partitioning of the main drive is not an option for me, beacuse I don't know how my regular files can grow, and a fixed division between regular and temporary files is always a waste of space. But splitting the backup drive may be an option. This split can easily be changed when necessary.

What do you recommend for such a long time backup of large data collections?

My first idea was, to make *two* partitions on the backup drive. One of about 40 GB for the mirror of the internal drive (only regular files, no temporary files). And one partition of 120 GB for saving several generations of my user files as disc images.

Best wishes
Jochen