Thanks for the update. I think the reason many of us avoid a clean install is the hassle of digging up serial numbers for apps that require licensing, reinstalling apps, and then adjusting them to the way we had them before and so on. But generally I agree, a clean install can cure many ills and get rid of a lot of unnecessary fluff.
As an Oracle DBA and developer for a Global Telecoms company looking after several thousand servers I learned to be very particular about stuff like that. All serial numbers, licences, login IDs and passwords were/are stored in an encrypted KeePass file. It's free, secure, fully cross platform including android and Apple ios and was the only application approved by the company. I find it invaluable.
I always look at any system/computer and my first question is always "How long would it take me to be up and running if it spontaneously combusts, or more realistically dies?" In my case it's only as long as it would take to get a new one out of the box, powered up and do a full restore from backup. All the important stuff is on NAS drives.
So many people buy a computer and just use it, they have loads of documents and photos running into the thousands and take no backups. Everything in their world is good right up until the moment it doesn't work and the realisation dawns that if it can't be recovered they've lost everything. Even if it survives long enough to be replaced the work involved in transferring their files to a new machine can be frustrating and take forever and they usually forget or miss something only to realise weeks later when it's too late.
What started out as a frustrating exercise in getting my iMac to dual boot has ended up being both interesting and with a Mac that runs like it did out of the box.