Should I Upgrade my 2009 iMac from Lion?

Hello All,

I'm struggling with the possibility of upgrading my late 2009 iMac Quad Core from Lion to the latest version (10.11?). There are a few reasons why I think I should do this

1. I can no longer upgrade iTunes
2. I seem to be having more and more connectivity issues with my two AppleTv's (AppleTV 2 & AppleTV 3)
3. Since I'm already several releases behind, perhaps there are other issues in the background running of my system that may be corrected
4. Perhaps there's a chance it will improve the performance of my system

I currently have 6gb of RAM running on the system, and actively have about 50gb free on a 1tb hard drive - I plan to migrate most of this to an external hard drive which will free up about 600gb, but cost is a factor to me, so unless someone wants to give me a 6tb external! If cost weren't a factor lets face it, I'd just go out and buy a new iMac! Currently I have my iTunes library spread across 3 harddrives (iMac & 2 external) but ideally I'll go to a single drive; that's another story!

Some things that I'm struggling with as reasons to avoid an upgrade

1. The old "if it ain't broke" mentality. Admittedly, it does perform a bit slower, but it is 7 years old....I got about the same amount of time on my eMac (2003 to 2010)
2. We know our way around iPhoto and was wondering if we would I have to upgrade to Photos, and if so, is it a smooth transition? Is there some prep work that could make this easier?
3. The big question, would the upgrade cripple my system? Would additional RAM help?
4. How integrated do I have to be on iCloud? I'm not too keen on going completely cloudbased? I back up my photos every month to a separate hard drive off site.

With regards to my AppleTV, are there any advantages from a connectivity concern? Will my WiFi be more stable for my AppleTV? It's not Apple Hardware (Linksys I think). I'm not able to hardwire as my house isn't setup like that, and the cost isn't in the picture right now.

Any help / tips / warnings would be appreciated!

Thanks,

mattfromcanada