I’ve actually done that...
Got so disgusted with the slowdowns that I bought a new one.
Admittedly, it was an excuse :).
The computer was 6 yrs old.
I put AVG and Malwarebytes and Spybot on my ten year old Dell, ran them every two or three days but still had bugs.
Got an iMac.
End of problem.
Better than re-formatting is getting an imaging program.
I use clonegenius (now called Data Backup Kit, http://www.spotmau.com/products/package/data_backup.html). It has bailed me out several times, and it has MY settings and installed software from the last time I ‘imaged’ my OS partition. I image every few months or after major software upgrades.
There are several ‘free for home use’ and pay version of imaging software.