You don't need to do a 'refresh install', I've been running Macs for something like seven or eight years now and I've never had to reinstall. When new versions of the OS come out, I just patch the new one. I've even just cloned from one Mac to another when I changed hardware.
I say I've never "had" to reinstall but I did one earlier this year just to see if I'd notice any difference and whether removing seven years of cruft would actually make any difference.
No. I didn't notice any performance difference between the two installations.
So just use your Mac and forget any Windows mindset where the computer slows down over time.
