There are a few possibilities to fix a messy backup solution.
For a continuous mirror, RAID 1 is your best bet. If you're constantly accessing the drive, an internal drive would perform much better. The only problem is you want to keep moving your drive away in case of a fire....
Maybe periodical Full backups with more frequent differential and incremental backups is better for you. The backup frequency is dependent upon the value of your data. If in a single week, you feel you create a substantial amount of valuable data, your backup frequency should increase. Remember, you can schedule backups manually as well after you've done very important work. DriveImage XML is a great full backup tool. For incremental backups, Freebyte backup is excellent (DriveImage XML may also have this feature). The point I'm trying to get across is, you can make a full backup every once in a while (say every 2 weeks) and store that somewhere else, and small incremental backups in between. Incremental backups take up less disk space than full backups, and are faster to perform.
Something else you might be interested in is syncing. You can make a full backup every 2 weeks or so with the registry and all, and then maybe just sync your new documents over the network to a NAS in another room. Synctoy is excellent for this and easy to configure.
Use whatever combination works best for you to ensure your data is safe and backed up. Just remember, more backups require more space, but space comes cheap, so backup as often as you can! There's an old saying that "Your data doesn't really exist unless it's saved in at least 3 places", which basically states that copies can easily be destroyed and lost. I try to keep true to this saying, and maybe others should too. ( Not mentioning any names! :) )