What are the Best Ways to Speed Up a Mac?
The only thing I can see which might help is freeing some space on your hard drive. 

With the lack of free space OS X won’t be able to make use of Virtual Memory as efficiently as it should, or possibly at all. I’m not 100% sure about Yosemite, but I’ve experienced a big performance hit on previous OS X releases when the OS can’t allocate as much RAM as it wants to. 

With tools like Photoshop, are you using a separate scratch disk? If not then you’ll be relying on the little internal storage available which will result in OS X having to free up RAM (rather than swapping it) to apply effects/filters/etc.