Is there a fix for my intolerably slow iMac?

Question

I will greatly appreciate any help provided by the community - whether it's harsh reality or a miraculous fix.
My beloved 24" iMac (Early 2009, 2.66 GHz Intel Core 2 Duo, 4 GB 1067 MHz DDR3, NVIDIA GeForce 9400 256 MB) - which ran like a dream all the way through 10.6.xx has been booted back to 2001 in terms of speed.  Even the simplest of things like opening Mail, launching Chrome or even copying files bring up the dreaded rainbow wheel and sometimes take 3-5 minutes to launch and return keyboard and mouse control to me. Photoshop and Aperture are virtually unusable.  A simple crop in Photoshop has caused a total system hang and working with any file over say 20MB in size becomes a game of patience, waiting and resisting the urge to put my fist through the glass out of frustration.
I'm a Mac user since 1993 and I've never been forced to downgrade the OS.  I've either ponied up and bought a newer model, or refused to upgrade the OS after learning a particular OS rendered my model unusable.  Well, I received poor information this time and this iMac went from a graphic and web production machine to being a glorified web browser (and even that is slow, jerky and unreliable).
Is there a cure for my woes short of trying to find my original install DVD and retrograding the entire thing back to 10.6?  I'm loathe to do this becaue this will render as useless several programs I use regularly - Coda for example and all of my Apple apps - iPhoto, Aperture, and who knows what else.  Based on the fact that I try to keep all my software current at all times, it could start an endless backward spiral that makes the situation even worse than it is already.
I am not in a position to upgrade with a new OS on the horizon and the current iMac crop aging as well - in fact, now would be perhaps the worst time to jump to a new machine.  Nor do I wish to lug this beast over to the Apple store and waste an afternoon waiting for a Genius to tell me to buy a new system.
I simply need to make the right choice this time instead of the wrong choice, which was installing Lion, and I could use some advice.
most sincerely,
Dave Bias

Answer 1

Well seeing as I'm running Lion on 2 GB of RAM, I can't see how upgrading the RAM will make that much of a difference.    If you are seeing launch times in minutes, it probably indicates your cache got corrupted by some third party cache cleaning software.  To see if some corruption can be fixed, first backup your data:
https://discussions.apple.com/docs/DOC-1992
Then boot in safe mode, holding the shift key.  If issues persist in safe mode, run the hardware test that came with your Mac. 
http://docs.info.apple.com/article.html?artnum=303081
And if that is unrevealing, and booting into safe mode doesn't solve anything, and you are backed up, try repairing the directory by:
1. Booting into the restore partition with command-R.
2. Selecting the installer's Utilities menu.
3. Selecting Disk Utility
4. Selecting First Aid
5. Selecting the boot partition.
6. Click on repair disk (not repair permissions)
Do NOT proceed with any install itself.  Just quit the install program
If the disk is not able to be repaired, purchase Alsoft Disk Warrior, and boot of that to repair the directory.
If it is able to be repaired, and the machine is still slow, I think you may have run into some RAM that is bad, and need to replace it, not add to it.
If Disk Warrior can't repair the hard disk, replace the hard disk itself.