Everyone "pooh poohs" it because OS X is not susceptible to the same rot as Windows - there is no registry - every app you install does not put it's junk all over your system files.

You're in a new world here - a lot of those things we use to do in Windows really do not apply here. And this is one of them.

As an old time gamer that was in the habit of doing a clean install of Windows about once every 6 months, I can testify this is a last resort with OS X and is extremely rare that anyone needs to do such a thing. I have not done one in over 4 years except after a new OS has been released. My wife's machine has now gone 4 years without a clean install and it has gone through 2 OS upgrades - try that in Windows - and still runs just as fast as the day it was brought home.

Having a backup of the original install is a bunch of wasted space on your drive. A clean install can be done in under an hour with your OS X discs.

What you need is a "backup" of your current up to date system, not a fresh install, so that if your drive dies, you're able to restore all your data. A backup on the same drive as your OS, is not a backup at all.

Even while you're saying you don't, have to say what you want is a bootable clone, not only for backup, but it comes in quite handy for troubleshooting purposes also.