My exerience with Dantz Retrospect is as bad as it can be. Concerning the disk space available nowadays I would recommend to regularly make a full copy of the volume to back up. For a 68 k Mac the backup of a volume usually will not be larger than some few GB, in many cases it will fit onto a single CD ROM. Better save the time for setting up some incremental backup solution that might probably not work in a case of need. If you want to have a simple mechanism to keep a folder on a remote drive synchronised, you could use Apples PowerBook File Assistant*. You might do some tests to clarify for yourself how the different rules to replace files work. You may let it's alias live in the Shutdown items folder.

*The File Assistant software is part of Mac OS 8.1. Easy Installation puts it only onto the drive of a PowerBook. Do a custom install or use the TomeViewer software to get File Assistant for a desktop Mac.