Why upgrade to Yosemite?

Question

I have the good fortune of knowing why not to upgrade. I had Mavericks already and I decided an upgrade might help fix some intermittent problems with my OS, like drag/drop being on/off.
Since upgrading to Yosemite:
Finder will not overwrite files (starts an endless loop and never finishes)
Finder will not open the preferences window
Finder will not shut down. Force quitting works occasionally, other times that too fails and I have to hold the power button until it shuts down the iMac.
HDD fan speed runs out of control after resetting SMC to try to fix some of the above
Bluetooth mouse now gets interference from Wifi, causing jerky movement while uploading or downloading
Transparency issues with the new interface, black corners instead of round corners, etc.
Possibly related, my USB drives now seem to disconnect intermittently as well (which throws a nice big wrench in my backup and flee plans).
After trying various fixes, removing software, reinstalling the OS, repairing permissions, etc. I have absolutely no solutions for the above except to backup everything, wipe the drive, and install the OS "clean".
I did so today and have already noticed the usual jumpy mouse when using Wifi.
And now file icons don't display correctly at small sizes, even after multiple cache cleans, a problem that numerous others have also experienced (along with more serious graphics issues, Finder performing like a wounded mule, Dropbox implosions, etc.)
All this and there's still an extreme poverty in actually helpful features. I'm still stuck with Maverick's butchery of the tags feature (replacing quick, simple, and visually useful labels with tiny colored dots that take twice as long to toggle was purely idiotic, in my opinion. Yosemite brings no reprieve.) There's still no "up" button for those that want Finder to just go up to the enclosing folder instead of picking from a dropdown list. I sincerely doubt that adding web searching to Spotlight is something I would ever want to use, especially since everyone privacy-minded is turning it off. And I'm incredibly uninterested in minute visual changes to add transparency, blurs and whatnot that you may appreciate once but that take up more GPU processing ever after.
So has anyone found any improvements in Yosemite? Please remind me why I shouldn't just do a clean install of Mountain Lion if I'm ever caught back up from the weeks I've wasted troubleshooting this dung heap.

Answer 1

How much RAM installed on your Mac.
How full is your Mac's hard drive?
If you have a long list of user login/startup items that launch at startup/login, you need to reduce the amount of these to around 6 or so items or less, if possible.
Do you have any unnecessary antivirus installed on your iMac?
Do you have so called hard drive/memory  "cleaning" apps installed on your Mac like MacKeeper, CleanMyMac 1or 2, TuneUpMyMac, MacCleanse, Memory Clean, etc.?
Have you updated all of your installed software and updated all connected third party device software and drivers?
Have you updated all of the various web browser plugins you that have installed within your web browser?
Do you use Google apps, like Chrome and Drive?
Ditch ALL Googlewares. They are ALL a serious resource hog on the OS X system.
If you do not like Apple's Safari web browser, download, install and try Mozilla FireFox, instead.
The current, up-to-date version of FireFox is fully compatible with OS X and is regularly updated by the great developers of the Mozilla group.