yes you do need to back these up.

1) Under Unix you can search for specific log files based on time stamp and copy only those that fall within a certain period of time (ie., find //*.* -mtime 0). That's one way of doing it. You need play around with it and make some assumptions about the length of time your backup takes unless you execute the archive search after the backup finishes and you have forced a logfile switch.

2) For us we backup the archive area each night for a month then we cycle through the process again. For us, we determined that we would not need archive logs from month to month. But thats a decision that took us some time to make given out environment and needs.

hth