That depends on how blindly and how completely you do it. If you follow this process, I think you're going to miss all the spyware / malware (and other crapware) that intentionally hides itself and slows down your system.
If you're deliberate about only backing up and saving the stuff you use, then you'll gain a lot of the benefit from the reinstall. The above isn't quite as deliberate as I'd usually like a user to be, but it's maybe a 30%-40% solution and is probably as 'automated' as you can make it. I know people that take days to reinstall every little thing.
As a Linux user, I keep a file in /home (which is a separate partition) that has my 'reinstallation script'. Every time I install something I think I'll need to come back to, I put the line(s) in my reinstallation script. Its about an 80-90% solution and as long as I stay within a distro family (I pretty much stay inside Debian, somewhere) I can just re-run my script and have most, if not all of my software back without an issue.