Shields up for the apple haters.  Lol.
Here goes:  My 27" iMac mid 2010 edition has recently experienced a slow down.  Wheel spinning having to be rebooted every 5-6 days to get it running smooth.  I'd say over the last 6 months or so.  In the last few weeks I have noticed some horizontal pixelation/nuances on the monitor on top of open windows and the desktop.  Often when this occurs the computer will lock up and I have to do a hard reset (hold power button down until it shuts off/ push it again to restart).  More often than not I have gotten a grey screen saying the computer failed to start because of a problem press any key to continue.  It goes through the boot up process again and works fine for a few days before it reoccurs.  I've been bad about leaving mail and safari up and running for weeks at a time.  I sit down at my desk do some browsing/checking email, etc.  Get called away for hours at a time before returning/resuming what I was doing.  I've done this since 2010.  Working from home guys understand.  Anyways I have gotten to the point lately that I just make sure all programs are closed before I walk away.  When I come back I open them again.  Not a big deal. More of a time waste than anything.  
I did some light researching and it appears my computer had a known graphics card issue that apple replaced if they failed early on and I am apparently well outside of the resolution window.  It appears the graphics card may be the culprit but I am certainly not the IT guy.  
What do you guys think?  I am good friends with a local computer repair business owner so I could take it to him.  Just trying to figure out if the problem is correctable and if so is the investment worth it in a 7 year old machine or should I just spring for a new one?