Yosemite screwed up my iMac

Question

So I decided to upgrade to Yosemite straight from Lion (Pls don't ask me irrelevant questions like why I didn't go through maverick, etc etc, I didn't feel the need to)
Now with 4GB of RAM, I have probably the slowest, the most frustrating computer on the planet,
1.  It's painfully Crawls, not even walks,
2.  Keeps dropping the WiFi connection randomly and more important, keeps FORGETTING my WiFi connections when it drops them, so I have to add the connection manually every single time.
3.  When I right click on a file, to chose 'Open with', it takes forever to 'Fetch' the list of applications that i can open the file with, sometimes even failing to do so, so I have click somewhere else and then right click again,
4.  When I open a folder, it takes forever to draw the icons and while its getting them to appear, the finder window is frozen,
5.  Everything, EVERY THING, crawls, opening any non-apple app is a nightmare, trying to open a microsoft office document completely make the iMac un-usable for like 3 - 4 minutes, Don't even ask about Google Chrome,
6.  I don't even use Apple Mail, which has been said to be the cause of the memory leaks and high CPU usage,
7.  Even the internet access appears slower compared to my windows PC,
8.  When I try to drag a window, any window, across the screen, it NEVER happens on the first try, because its frozen, specially apps like photoshop, chrome, evernote, etc.
Now I have tried almost ALL the solutions popular on the internet, including turning off the bells and whistles by reducing transparency, changing the dock pop-up effect, rebooting into safe mode, fixing my disk permissions, resetting my System Management Controller (SMC), resetting my PRAM, replacing the Network Configuration & Preference Files for WiFi, switching to G band, Creating a New Wi-Fi Network Location with Custom DNS, whatever i could find on the internet, including this forum,
Everything except a clean install, but Nothing. The machine I have here is NOT the Mac I used to have and like. It *****.
This same iMac was what i used to call 'Awesome' just before this update when it had Lion.
Even TEXTEDIT takes like 30 seconds to open and shows a spinning wheel for like 10 seconds, for god's sake.
Why is Apple always so Dumb, Arrogant, Un-responsive to user's problems, aren't they making a **** lot of money already from us ? Can't they hire better brains who'll not push out updates before they are tested across hardware ?
Or at least some PR staff who listens to user's feedback on their own forums and responds, not in copied-pasted dumb text from their website though, instead of sitting around in their offices playing on their iPads ?
If an OS is SO resource-intensive, why push it to older models, do they want to make everyone buy more RAM and newer hardware every time something new comes along ?
I'm regretting trying this update. Could anyone please advise what's the best way out of this mess ? Would a Maverick clean install be good for a mid 2010 intel iMac ?
Hardware: 3.06 GHZ Intel Core i3, 4 GB RAM,
Apps most used: Chrome, Photoshop, Evernote, Textwrangler, iTunes.

Answer 1

Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen. Click the Clear Display icon in the toolbar. Then take one of the actions that you're having trouble with. Select any messages that appear in the Console window. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
Some private information, such as your name, may appear in the log. Anonymize before posting.