Sure it'll be faster but you really want to drop $$$$ on new machine that you use for surfing the web, emails and occasional photo management?
Typical forum advice to replace your perfectly working machine with new one, this amazes me. Each to his own what he/she does with hard earned cash but this behavior is just pure consumerism.
I have 2009 Macbook Pro that I bought second hand, I do live AV sets with it (video mixing in real time) and sometimes even edit HD videos on it for christ sake. I put 8 gigs of RAM in there and it runs Mountain Lion just fine, I have Adobe CS5 on it that works OK.
Your iMac is beautiful, 27 inch machine that will easily run for another few years. Sure, maybe you won't be/shouldn't be upgrading to the latest OS when it comes out but you can still use it as you're using it now (hello 10.6 users).
Your computation needs could be met with a very cheap and old PC for that fact, you don't need core i7 and great graphics card. If you want to make your iMac feel younger and snappier, replace the hard drive with SSD, it will feel like a brand new computer after the upgrade.
Some of the forum members are just ridiculous with their advice.