Upgrade RAM/SSD or Buy New?

I have a mid-2009 13" MacBook Pro running on Snow Leopard (10.6.8), 2.53 GHz Intel Core 2 Duo, 4GB RAM and 320GB HD. I have bought a new DSLR and I understand the raw files won't open on my Adobe Photoshop Elements editing software. To install the latest version of my software, I will need to be running Yosemite or El Capitan. I'm concerned that if I run El Capitan, the laptop will run slower than it is currently on Snow Leopard.

Firstly, should I upgrade to El Capitan and see what happens, or should I increase the RAM or swap to SSD flash storage? I've had this laptop for 6 years and it's been fine until recently when I noticed Safari won't connect properly and loads with errors. It is also rather slow. I have started using Firefox instead which is moderately better, but is not without similar issues. If I were to upgrade, what would give me the biggest improvement in terms of speed, fixing my web browsing and improve the editing of multiple large raw files? Either upgrade RAM first, then swap to SSD or vice versa or both? How long will my laptop last once upgraded?

Or is 6 years getting on a bit and I should consider buying a new MBP? The problem is I would like to upgrade to 16GB RAM if buying new, but cannot afford to stretch to 512GB flash storage. I currently house all my photos and videos externally already and use 190GB of my 320GB HD. I'm worried 256GB flash storage would not be enough. How much free space is optimal for running OS X? A 13" MBP/16GB RAM/256GB plus Applecare costs £1560 already. To upgrade to 512GB storage is an additional £200 which is beyond my current reach.

Please, any advice would be much appreciated. I'm a first time poster, sorry for the long question.