I've seen 4.5 GB System Restore on one of my own machines before trimming, and I've seen forum posts about 15-20 GB of Restore.
I too have SysRestore disabled, but my data and image backups are all external, i. e., to Flash, CD, or DVD. I agree that backups to an internal partition are even faster, but have you considered that if it is your HDD that fails physically, rather than a sw corruption, the backup partition may be of no use, depending on the degree of damage? It might need a clean room with bunny-suit people -- very expensive :-)
I didn't pay up for a large HDD. I bought the cheapest model of this rather low-end machine, and that's what it came with. I paid a few dollars for an after-market RAM upgrade, which enabled the disabling of the pagefile. This made a huge increase in speed, and, I am told, saves considerable wear and tear on the HDD, as RAM is constantly reading and writing to the disk (pagefile.sys). No more.
I agree your disk usage is still very reasonable and that you should have fast internal backups. I see posts at other forums complaining that they have problem X, and they have only 9GB HDD space left, please help! I just kind of got into this frame of mind that "If you don't need it, why are you carrying it around?" E. g., in Win XP SP2 there is a text editor designed for people migrating from Win 3.1 to 95; there is a file (C\Windows\System32) traffic.dll which is used only in the Microsoft® Flight Simulator® game. Probably only 0.01% of all buyers of XP will buy that game, but the file is there anyway.
It gets to be kind of fun after a while, seeing what ridiculous and obsolete garbage is in there, along with legitimate files for functions that I don't use and never will. Program files are almost as bloated sometimes. E. g., Microsoft® Office 2007® > 700 MB. Open Office, which is free, is about 280 MB out of the "box". I have it down to 142 MB. So, I guess it's become sort of a hobby -- in the words of Antoine de Saint-Exupery, "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." None of my own data have been sacrificed.
Thoroughly enjoyable chatting with you. Cheers!