No, actually, it's not. Whatever security software people who get this "crap" are running, it's obviously ineffecive. And the "reasonably savvy" would never click on some unknown downloader and expose their OS willingly.
The bottom line is to invest in some sort of "ghosting software" that will image your healthy drive (much faster than "backup" software), to an external drive. You then have to keep the image up to date (depending on how often you install/update programs, download new data files, etc.). If disaster happens, then you can relatively quickly re-format the main drive, re-install the image and be up and running again.
The initial expense would be quite a bit less than $300.
Sorry to be so blunt on this, but the more people who leave machines "exposed and neglected for years," the more of a national security threat it poses -- evidenced by the recent DDOS attacks on Georgia servers. All of the attacks weren't coming from conscious actors. It's estimated that a ridiculous amount of oblivious home users, worldwide, are running infected systems which are potentially attack vehicles for whomever happens to "pawn" their systems.
And related to your comment, the Folding@Home stuff hardly seems worth the network risk....
Exactly right. The Washington Post did something useful for once, and ran an article about botnets:
Invasion of the Computer Snatchers
Good intro for users.